A one-time amphibian farm, growing everything from poison dart frogs to snakes for export to the United States, Sabalos Lodge (tel. 505/8850-7623, Managua tel. 505/8823-5514 or 505/2278-1405, sales [at] sabaloslodge [dot] com, www.sabaloslodge.com , $35–70, includes breakfast) now focuses on tourism, with 10 riverside bamboo and wood cabins with thatched roofs, hammock lounge, and a dining area.
The meals and the service are excellent, $5 for breakfast and $10 for lunch and dinner (huge portions). Hiking trails and inner tube floats are available, plus three pangas for pickups from San Carlos  and tours to the sunken ship, nighttime caiman-watching, and more; also tours to Indio-Maíz biological reserve, kayaks, and horses.
The lodge is a five-minute boat trip (or 15-minute walk) downstream from Boca de Sábalos .
The lodge is associated with the private nonprofit, nonpartisan San Juan Rio Relief (sanjuanriorelief [at] cox [dot] net, www.sanjuanriorelief.org ), a team of dedicated people from the U.S. and Nicaragua who came together in 2003 with the goal of bringing free medical healthcare to the people of the Río San Juan.
Located downstream from Boca de Sábalos on river right (before reaching El Castillo), Montecristo (tel. 505/8649-9012 or 505/2583-0197 in San Carlos, montecristoriver [at] yahoo [dot] com, www.montecristoriverlodge.com , $65 all-inclusive) is a calm, riverside resort offering sportfishing, birding, hiking trails, horseback riding, and tours of local cacao farms and reforestation projects; a variety of rooms on a neatly kept compound and private nature reserve of 120 acres.
They can also get you to area reserves and Solentiname. Your all-inclusive package includes three meals, horses, boats, and other activities; ask about discounts.