During a previous trip to Chiapas; on our drive from San Cristóbal de las Casas to the airport in Tuxtla Gutiérrez we drove across a bridge that spanned a gorge in the Grijalva River that took our breath away.
After we arrived at the airport that day we talked to other passengers on our flight whose whole purpose of traveling to Tuxtla Gutiérrez was the chance to take the river tour of the Sumidero Canyon (Spanish: Cañón del Sumidero). So the seed was planted that on our next trip to the area, taking the tour was on our must do list.
Most travelers wanting to visit the canyon will book a tour that will probably be packaged with lunch and about an hour of sightseeing around the town from either Tuxtla Gutierrez or San Cristóbal de las Casas.
But as discussed on the Chiapa de Corzo page of this website; rather than take a day excursion with a bus-load of other tourists, our plan was to spend a night in that town so that we could be on the first boat to take the river tour the next morning.
So on our first (and only) morning in Chiapa De Corzo we made the short walk to the river front where we found the ticket office and the pier where the tour embarks. We arrived around the stated opening hour of 8:00 AM, bought our tickets for 190 MXN Pesos (or slightly over $10 USD at this writing) and waited for the first boat to fill its 10 seats, which took 45 minutes to an hour. Once full, floatation vest were handed out and we headed off down the river. I should point out that avoiding the wait we experienced is one advantage of booking with a 
tour group as you’ll be bringing enough people to fill a boat with you.
The 2-hour boat ride through the Canyon was great. You would be smart to bring sun screen, a hat and some water as you will be in full sun for most of the tour. We saw dramatic scenery, amazing bird life including flocks of white herons and cormorants as well as occasional sightings of a hawk (more correctly a kite). Plus we saw crocodiles in a couple locations.
My words really don’t do the experience justice so on this page you’ll find lots of photos. If you click on any photo they will link you to a larger version of the same photo and access to the Sumidero Canyon section of our flickr page, where you can find additional photos.