The River Tables.
If a per-country table listing gets you what you want to know, click on the country to get it: Chiapas Guatemala Belize Honduras El Salvador Nicaragua
The River Maps.
Clicking one of the following links will open a google map showing the location of all the runs in mayanwhitewater-land, plus river gauge and weather station locations. Yes, there are a lot of runs around here! Option (2) takes you directly to maps hosted by google, split up by category and which may load easier for you (without tracelines). Option (3) allows you to download a file suitable for viewing the markers directly on your Google Earth client (but you will have to update manually).
(Note markers are color-coded: class I, class II, class III, class IV, class V, class "VI". Markers with a black star inside indicate rivers with a write-up.)
(Note streamflow gauges are also color-coded: "interesting" flow, river is up in the last 2 days, uninteresting flow (or uncalibrated), only uncalibrated height readings available, no recent flow or height readings available.
(Note rain gauges are also color-coded: means good rain yesterday, means little or no rain yesterday, and means recent measurements are unavailable.)
(Note further: Google Maps labels a lot of towns/villages incorrectly)