Lake Nacimiento is a lake that has been through a lot over the years. In the early 90's, the lake was known for excellent smallmouth bass fishing with solid northern strain largemouth mixed in in good numbers. Catching a 3lb smallmouth or a 6lb largemouth was not anything to write home about during those years.
In the late 90's however spotted bass and white bass took over, and changed the dynamics of the lake. Both of these species are voracious, reproduce rapidly, and known for out-competing other species. Nacimiento is now known best for numbers fishing for these two species. It is not uncommon to catch 50-100 spotted bass in a day at the lake, just don't expect very many of them to be over 2.5lbs.
Nacimiento is also subject to large fluctuations in water level. During high water years, the spotted bass and white bass thrive and grow fat. Winning tournament limits for 5 bass may range from 12-17lbs during these good years. On low water everything in the lake struggles and winning bags may be 9-11lbs. The cycle of boom to bust can be rapid at Nacimiento.
Primary forage in the lake is threadfin shad and crawdads. Popular lures focus on these two forage bases. It is not uncommon to see busting bass and white bass in the summer and fall months chasing packs of shad. It is also normal to see bass with their faces scratched to bits from digging for crawdads in January and February as the lake rises.
Channel catfish and crappie are also present in the lake and catfish fishing can be good in the backs of coves and around docks. Crappie are a boom and bust fish and have not been very prevalent in the lake in recent years. They are in there though.
The lake in general is rocky, with gravel, chunk rock, and sheer rocky cliff shorelines. Stickups and laydowns are present on high water, but you can expect to fish rock bank most times of year. Clarity ranges from muddy during winter, to 10 feet or more in the warm months. Nacimiento gets tremendous pleasure boat traffic in the summer so expect mud lines to be a factor any time from April through September. On holiday weekends in the summer, this is one to be avoided.
One final thing to mention is the spring white bass migration to the river. Nacimiento is the only lake in the state with white bass, and if you did not know - they spawn in the spring by the droves. Check the Nacimiento river starting in mid-March. If the water is clear you may be able to sight fish for them. Fly fishing for them is a popular option. The whites can get up to 2-4lbs and they fight hard. Any white bass caught and kept must be killed immediately. DFG does not want these fish spreading to other lakes.