See here for my notes on in-river hazards and what not to assume about my river write-ups.
Spanish is the predominant language in the MayanWhiteWater world, except in Belize where many speak English, and in many villages in Guatemala, where one of 21 Mayan dialects or other languages may be spoken. But in general, Spanish will get you by, and it is difficult to get around without some. Fortunately there are many cheap language schools in the area, and I recommend taking advantage of them for a week or so if you plan to spend much time travelling around.
First-time visitors to Central America will inevitably come down with travellers' diarrhea or worse. Paddlers are exposed to an extra source of water-borne parasites and bacteria, and paddlers staying more than a week have a 50/50 chance of picking up an intestinal bug. Diarrhea lasting for more than 3 days is your sign to visit a doctor, who usually will know just the drug for you.
Though civil wars and other area-wide conflicts are a last-century thing, Latin America is generally not as safe as the United States. But with a bit of luck and taking a few common-sense precautions you will avoid any unpleasant situations. Of course in touristy areas watch out for pickpockets and avoid empty city streets at night. Also don't leave your car on the street at night. The capital cities of all Latin America countries are particularly crime-suffering and there are definitely certain of their neighborhoods you should never enter. The violent crime that you read about in the papers is not tourist-targetted. In general, rural areas are safer than cities, but on rare occasions nasty incidents do happen: buses get held up, groups get kidnapped, female travellers get raped. Reading the State Department warnings from the U.S. or the E.U. in recent years is enough to frighten even entrepid travellers, but they generally exaggerate the situation.
Kayakers and other adventurous types have the advantage of showing up in places where they are not expected, and we generally enjoy a warm welcome. I personally have never been held up, despite 9 years of travelling whereever and whenever I felt like it, often times solo. Crime is often random, localized, and a game of chance, no matter where you are in the world. My suggestion is to ask the locals if you are unsure of a particular road or area. Some command of Spanish is quite helpful.
The growing drug trade and drug violence, while alarming, also does not pose an imminent threat to kayakers or other tourists, unless you are poking around the Mexico-Guatemala border in a wrong-place-wrong-time scenario. Again the locals are usually the best source of information. If I become aware of any place to avoid in the future I will mention it here and in the corresponding write-ups.
Despite the generally hospitable nature of Central America, there are some rural areas of Chiapas and Guatemala where strangers are not immediately welcomed. These are areas where the locals have organized against damming and mining interests. Any stranger entering these areas is immediately suspected of pertaining to these interests, and may be confronted or even detained, to be brought before a town council meeting before being released. In Chiapas this can happen in Zapatista-controlled areas, usually signed, and in Guatemala this is most common in the departamentos of Huehuetenango, Totonicapán, and Quiché. In these areas you may want to ask if the local people are "delicada".
In addition, in some (non-touristy) rural areas of Guatemala a paranoia about strangers "stealing babies" has developed over the years. Surprise visits by outsiders can awaken this paranoia. Tourists should be sensitive to this when they approach women and children in the countryside.
Note that these issues only pertain to a small fraction of the runs; if a river passes through a sensitive area, it will be noted in the per-country tables and in the write-ups.
The entire area is lacking in coverage (hence this website and my desire to write a guidebook). There is a 2000-edition guidebook for Mexico called A Gringo's Guide to Mexican Whitewater by Tom Robey which includes the main jungle rivers in Chiapas. For Honduras there is a 1997-edition book called Honduras: The Undiscovered Country by Andrew Hibbard of Ríos Honduras which describes 17 rivers (noted on the Honduras river table). That's it.
In case you're interested in what others have written about the area's whitewater, check out this list.
A good road map is a must for any boater, and the basic tourist ones often won't do. In Mexico, pick up a good road atlas. In Guatemala, pick up the excellent International Travel Maps-produced map. In Belize, the best one is published by National Geographic, but really any map will do, there aren't many roads anyway. In Honduras and El Salvador, I have yet to find an adequate map; the most complete ones are the "official" wall-sized maps sold in their respective Geographic Institute offices.
For serious exploring you may want to look at the topos. 1:50,000 topos are sold in each country in their respective Geographic Insitute offices (for about $8/each), and in most offices you are also allowed simply to browse. In Chiapas, go to the INEGI office at "6a Sur Pte #670" in Tuxtla Gutierrez (or if they are closed another option is the Central Public Library at "Blvd Corzo & 11a Ave Oriente"). In Belize, go to the Ministry of Natural Resources and Agriculture, Land Information Center office, Queen Elizabeth II Blvd (end of Belmopan Hospital street), Cohunewalk, Belmopan. In Guatemala City, go to the IGN office at "Ave Las Americas 5-76, Z13". In El Salvador, go to the IGN office at "1 Calle Pte & 47 Ave Nte" in San Salvador (here they will not let you just browse). In Honduras, go to the IGN office in Barrio La Bolsa in downtown Tegucigalpa. OmniMap also advertises topos for all these countries on-line (http://www.omnimap.com/catalog/int/topo.htm).
To translate my metric meters-per-kilometer gradients into feet-per-mile, multiply by five; E.g., 10 m/km = 50 ft/mi.
If you have your own car, but don't have a driver, you can usually find one easily through a local hotel or business. $10-$15 per day will usually do it. Taxi drivers are also reliable but usually want more like $20 or $30 per day (in your car). Before you put-on, make sure to note the driver's phone number, and carry some money for emergencies. Agree on contingency plans.
If you don't have a car, you can usually easily find a pickup and driver to take you, but it won't be cheap. Or, if your access points are on public bus routes, you can use public transportation. I mention this option, when available, in the write-ups. The general problem with buses is that put-ins are often in mountain villages with limited service in the mornings (most buses leave the villages in the morning and return in the afternoon).
Central America enjoys warm, tropical weather, though the temperatures vary some by season and elevation. The year is basically divided into a dry season and a rainy season (see below). It is always warm near the coasts, but it can be quite cool up in the mountains, especially so when cold fronts come through from December to February. The warmest time of the year is the end of the dry season (March to May), when there are few clouds and rain to cool things off.
You may hear people talk about a "canícula", which means an extended period (10 days or more) with little or no rain in the middle of the rainy season, often happening in July and/or August. You don't want to hear that word.
The most dramatic weather phenomena are hurricanes and tropical storms/depressions. These can bring a lot of rain, usually to one side of the continental divide or the other. One good source for keeping up with the current weather and understanding these storms is Jeff Master's blog on Weather Underground.
There are a few rivers that run year-round, but most rivers run only during the rainy season, which on the Pacific side is June to October, and on the Caribbean side is July to January, with some areas receiving rain into March. From June to October the biggest generator of precipitation, apart from hurricanes, is the daily tropical water cycle which brings afternoon and evening rains. From November to February the biggest rain generator, felt mostly on the Caribbean side, are the northern cold fronts which mix with the region's warmer/humid air masses to produce more spotty rain.
The peak of the water in all areas is mid-September to mid-October, when everything but the smallest creeks will have boatable flows (a few rivers may even have too much water). The smaller creeks can go off at any time during the rainy season, they just require the luck of several days in a row of heavy rain, and only give you a 1 or 2-day window to catch them.
On-line river gages (see below), rain gages, weather stations (mostly from WeatherUnderground.com), and infrared radar are helpful for guessing how the water is in a certain area. The gages and weather stations are marked on my maps. The river gages give you the most reliable information on how the rivers are flowing, but their coverage is limited. Regional infrared radar is supplied by NASA, where you can see the rainfall for the last 7 hours.
In Chiapas, the weather (and river) agency is called Conagua. At the bottom of their daily weather bulletin there is a "isoyeta" (isopluvial) map of where rain was seen the previous evening. They also list rainfall for 6 major cities in Chiapas, which I collect and graph (30 days) on my maps. The map icons are color-coded: means good rain yesterday, means little or no rain yesterday, and means recent measurements are unavailable. For Guatemala the weather (and river and earthquake and volcano and tidal wave) agency is INSIVUMEH. They provide an isopluvial map for yesterday or the past month. Their weather forecast bulletin page also lists (only in the morning) yesterday's rainfall for major cities, which I collect and graph on my maps also.
There are several on-line sources of weather forecasts, though I tend not to rely on them too much since rainfall can be so spotty. There is an interesting 4-day regional graphical rainfall forecast that gives a false feeling of certitude about where the rain will be but is better than nothing. Maybe the most informative (in Spanish) is Conagua's weather bulletin for Chiapas, except when it hasn't been updated for a few days. Weather.com and Weather Underground will give you forecasts for selected cities. I also look at the Guatemalan weather agency forecast (in Spanish) for the day, work week, and weekend. The respective Salvadoran agency has some kinda-interesting charts of flow predictions if you poke around.
For those hungry for more information, NOAA's Model Analyses and Guidance (MAG) website also supplies some on-line numerical models of rainfall (and other parameters). These models are getting better all the time. You can go directly to the map of interest for Central America here, then you select the model and then the time range on the PRECIP PARAMS line.
Tropical storms and hurricanes, especially prevalent on the Caribbean side, can have a lot to say about water levels in the rainy season, but are not very helpful for boaters. They bring the threat of severe flash floods and washed-out roads. In general, however, having too much water in a river is rare (at least in the morning). See this page for warnings about flash floods.
There are two places on this website where I indicate the boating season for any particular river. The first is in the per-country tables, where each region has a season specified. The second is in the river write-up (if one exists).
In mayanwhitewater-land there are several networks of on-line gages maintained by the respective country's weather and electrical agencies. In Central America many of these are sponsored by the good 'ole USGS. (You can see their page at http://pr.water.usgs.gov, also NOAA maintains links to some of the same data. You can see the river levels up to 4 months back, and in some rare cases, a calibrated flow reading.) The gages have a placemarker on my maps where I have consolidated all the known available data, with current readings in the bubble, links to any pertinent site, and any historical data that I have. Also in the write-ups I try to link to the relevant gages and what gage heights to look for.
Even if the gage is functioning correctly, the actual flow is usually unknowable, since the calibrations may change flood-to-flood. So at least as interesting as the actual gage height number is seeing the rise and fall pattern of the past week (for USGS gages where you can see hour-by-hour activity), since almost all the runs are rain-dependent. If the river is going up and down significantly most days, that's a good sign of heavy rain and a good chance to catch a boatable flow.
Gages with placemarks on my maps are color-coded according to the flow readings: means "interesting" (high enough that some run in the area is up), means "interesting" and the flow went up in the last couple days, means "uninteresting" (low), means no up-to-date flow readings are available, means no up-to-date flow or height readings are available. However, many of the gages I have not calibrated or verified, which means I'm doing a lot of guessing.
Following is the detailed description of where I find the data for my links and graphs:
In Chiapas, streamflows for some rivers are monitored and published by Conagua in a daily report, which I save on my server daily (the historical data is not easily available from Conagua). Many of the gages have a flow reading; the others have a height reading which may give you an idea if the water is up or down. The interesting gages have their own markers on my maps, where I place an up-to-date flow graph that I derive from my database. Some of the gages, especially on the Pacific coast, were damaged by Hurricane Stan in 2005 and have yet to be repaired.
For some rivers in Chiapas I have been able to obtain historical flow data from INEGI and the charts are presented in the river descriptions and gage placemarks. I have noticed that on average the historical flows are higher than what I've seen. Either 1) rainfall happens to be less this century, 2) streamflows are decreasing over time, or 3) many gages weren't calibrated accurately.
In Guatemala INSIVUMEH is the river gage caretaker. Many of the gages were knocked out by Tropical Storm Agatha in 2010. There are links to most of the gages on the USGS page, plus a daily Insivumeh report of river heights for those and a few more gages (I make 30-day graphs of this data available on the maps). The electrical agency INDE offers one more interesting graph of recent flows on the upper Chixoy (aka Negro) River here.
In El Salvador the agency responsible for the gages is SNET. They maintain their own 7-day graphs of the available gages which are clickable off their daily river report, or you can see most of them (not all) on the USGS page.
There are no on-line gages in Belize.
In the write-ups I give water quality ratings ranging from good to poor. There are many more rivers with poor water quality than with good water quality in Central America. In fact no river here can be considered pristine or safe to drink. Human, animal, and agricultural waste are the main culprits. Personally I am willing to put up with a bit of trash in the bushes or float by women doing their laundry in the river, but even I have my limits. A few rivers, usually downstream from large towns and cities, are so polluted (smelly/sudsy) I have not even bothered looking for put-ins. But be warned: you swallow a mouthful of water in most rivers around here, you will suffer the consequences which often involves prescription drugs. I recommend noseplugs too.
Note: water color is not very indicative of water quality. Many of the rivers down here run brown in the rainy season which is due to natural sediment. That said, clearer water in some cases indicates spring sources, which is indeed cleaner than rainwater run-off. Also, water temperature is a big indicator. Warmer water harbors more bacteria, whereas colder water indicates higher elevation or spring sources.
Disclaimer: all information provided in the MayanWhiteWater.com website is provided without warranty of any kind. All decisions you make on and off the river are your own. Do I really need to write that?