The world record bigmouth bass was caught in SD, lots of good fishing...
I used to fish Cuyamaca a lot, I worked there in high school back in the old days, good bass
If you camp at the Lake Jennings campground you can fish on their side of the lake with no fishing fee
There's also a county campground at Lake Morena (right below Corral Canyon). The best camping spots are the first few on the left, walk to the lake in the morning, wheel in the afternoon and then a little sunset angling.
Some spots at Otay on the north side are a short walk from parking spots
SD County has a campground at Guajome, just east of O'Side. There is a small lake there, tons of bluegill, some bass and cat, sort of meh fishing last I heard
Clickable Links to SD Lakes and Fish Reports