The Naujan Lake, the fifth largest lake in the country, is a large freshwater lake probably of volcanic origin, extending for about 14 km from north to south, and seven km from east to west. The lake is fed by local run-off and there are no major affluents; the outlet is near the north end through the Lumangbayan River. The eastern shore is precipitous, but to the west the land rises gradually and there are large areas of shallow water with an abundant growth of aquatic vegetation. There are several hot springs along the eastern shore.

The lake is also rich in nutrients and supports a major fishery of both demersal and pelagic species. Most of the inhabitants of the region depend on the lake for their livelihood. The locals use the lake as a communal fishing ground. The marshland adjacent to the Lake remains under grass and sedge.The dense cover serves as habitat to resident and migratory waterfowls. The presence of wildlife also enhances the value of the Lake as a recreational area.

The lake is part of the Naujan Lake National Park (21,655 ha), established under Proclamation No. 282 on March 27, 1956 and was consequently amended by Proclamation No. 335 on January 25, 1968. The lake is open to commercial fishing subject to the following limitations:

(1) permits must be renewed annually;
(2) there are bag limits for certain species not included in the list of protected species;
(3) fishing is only permissible between the hours of 4.00 am and 5.00 pm;
(4) no fishing is permitted in the marshy area of the lake which has been declared a fish sanctuary.

Unfortunately, the enforcement of these regulations and other park regulations is reported to be extremely poor. Because of the increase in the human population in the area, the demand on the lake’s natural resources has grown rapidly. Fishing is intensive and there is continuing conflict between preserving the National Park for wildlife and development of the area for commercial and subsistence level activities by the local residents.

The privately owned fish corral built at the mouth of the Butas River with Government approval constitutes a major threat. Its massive door is opened during high tide and then closed, blocking the exit of marine species in their migration to the sea to breed. The small population of crocodiles, although protected by law, continues to be persecuted; fishermen catch young crocodiles on fishing lines and large animals are killed in nets.

The Bureau of Fisheries and Aquatic Resources has a Limnological Laboratory and Experimental Fish Pond at the lake.

The park is good for outdoor recreation like boating, picnicking, bird-watching, hiking and research.