Where, in fremont, ca, can a female swim without feeling insecure?

I can't offer and specific places to swim out in California (I only live in Connecticut!) but what I can tell you is that insecurity is a personally specific feeling only experienced by those who have a general feeling of instability and/or jealousy. If you can get over these feelings then you'll realize that you don't have to feel insecure in 99% of the environments that you encounter (both instability and jealousy are controlled by dominant forces and if you conquer these dominant forces then you'll cancel out both).