Lake Jennings is a reservoir operated by the Helix Water District.
It is surrounded by a walking path/trail. 
An RV/tent campground is on the NW side of the lake. 
This is one of the most beautiful environments I've seen here in San Diego.

My wife and Debby doing silly exercises in the park campsite.

We made a rare dawn visit in order to get to the lake proper (not campground).

 It was worth it!