Poway's lake adjoins a city park, and is free for Poway residents. 
I think they allow free access to non-residents on weekdays, but charge on weekends. 
It's a bit more park/less lake for my taste, but then I'm not a resident.

We were astonished to see so many birds. Not just ducks, but vultures, 

osprey and a bald eagle.

We walked around the lake in April 2024 and found it to be beautiful at 8-11 am. 
But I'd advise caution, carrying water, and sun protection later in the day.