On the downstream side of the San Blas  bridge over Estero San Cristóbal, launches-for-hire will take you up the Río Tovara, a side channel that winds about a mile downstream into the jungle.
The channel quickly narrows into a dark tree-tunnel, edged by great curtainlike swaths of mangrove roots. Big snowy garza (egrets) peer out from leafy branches; startled turtles slip off their soggy perches into the river, while big submerged roots, like gigantic pythons, bulge out of the inky water. Riots of luxuriant plants—white lilies, green ferns, red romelia orchids—hang from the trees and line the banks.
Finally you reach Tovara Springs, which well from the base of a verdant cliff. On one side a bamboo-sheltered palapa restaurant serves refreshments, on the other families picnic in a hillside pavilion. In the middle, everyone jumps in and paddles in the clear, cool water.
You can enjoy this trip either of two ways: the longer, three-hour excursion as described ($40 per boatload of 6–8) from El Conchal landing on the estuary, or the shorter version (two hours, $30 per boatload) beginning upriver at road-accessible Las Aguadas near Matanchén . Either drive, taxi, or ride the blanco (white) bus or the navy blue Transportes Noreste bus.
The more leisurely three-hour trip allows more chances (especially in the early morning) to spot an ocelot or crocodile, or a giant boa constrictor hanging from a limb (no kidding). Many of the boatmen are very professional; if you want to view wildlife, tell them, and they’ll go more slowly and keep a sharp lookout.
Some boatmen offer more extensive trips to less-disturbed sites deeper in the jungle. These include the Camalota spring, a branch of the Río Tovara (where a local ejido maintains a crocodile breeding station), and the even more remote and pristine Tepiqueñas, Los Negros, and Zoquipan lagoons in the San Cristóbal Estero’s upper reaches.
In light of the possible wildlife-watching rewards, trip prices are very reasonable. For example, the very knowledgeable bird specialist Oscar Partida Hernández (Comonfort 134 Pte., tel. 323/285-0324) will guide a four-person boatload to La Tovara for about $50. If Oscar is busy, call “Chencho” (tel. 323/285-0716) for a comparably excellent trip. More extensive options include a combined Camalota–La Tovara trip (allow 4–5 hours) for about $40 for four or Tepiqueñas and Los Negros (six hours, 7 a.m. departure) for about $60.