Morena is one of the oldest reservoirs in San Diego County. 
It receives its water from rain and runoff, so the water is inexpensive 
compared to that imported from California aqueducts. 
How cheap? Approximately $200 per acre/foot versus $800. 

We did a 15-minute (free) tour by truck and camera on our second visit:

About 10 months prior, on our first visit, we stayed half a day. 

We rented a boat and spent some lovely hours 
putting around in the sunshine.