Just go to the City Hall and tell them you would like a key to Baja Beach. I think they are about $25 a year. They change the lock in October and that is when you have to get a new key. Call them and find out when the key changes. Here is the phone number 817-249-3000
Here is the address for the City Hall 911 Winscott Road, Benbrook, TX 76126
I have alway enjoyed going kayak at the dam. It would be a good place to bank fish too.
Let us know what you find out about the key.