The favorite freshwater fishing spot in Costa Rica is Lake Arenal, located at the base of a volcano in the San Carlos Valley. Rainbow bass, ranging from a average 5 pounds to an extraordinary 10 pounds, are abundant in this lake. The rainbow bass, fished the same way as large mouth bass, is a member of the cichlid family and first cousin to the peacock bass.
Rainbow bass can also be found in the rivers of the eastern seaboard, especially the Caño Negro Lagoon and its tributary rivers near the border of Nicaragua and Lago Hule, near Cariblanco. The Caño Negro Lagoon is enormous and well known for its huge tarpon, snook, guapote, drum, and others. The road into Hule, however, is treacherous. Many enthusiasts would suggest taking the trek, a mere nine kilometers of dangerous driving, with no less than two 4-wheel drive vehicles going together.
Rainbow trout are plentiful in the Río Chirripó Pacifico in San Gerardo de Rivas. This is located at the entrance to Chirripó National Park. Small rainbow trout inhabit the Savegre River just below San Gerardo de Dota. An hour outside of San José, off the road to Tapantí in the Orosi Valley, there are private ponds along with places to rent gear. Also try the Cerro de la Muerte and in Copey de Dota. These private ponds charge a fee of about $7 per kilo for whatever you pull out.
There are many more rivers that are good for fishing, and contain a variety of fish. Guides are available too, some specializing in fly fishing and float trips.