The pollution that closes beaches can be avoided with better sewage treatment facilities. Who should bear cost?

OK, here are some possible answers to your question. For each one, you'll have to evaluate it and determine if it is "fair"....

1. The users of the beaches should bear the cost by paying a use fee.

2. The beach is an asset for the city that owns it and the sewage is reaching the beach through city utilities and drains. Therefore, the city taxpayers should pay for the cost, even if they themselves do not use the beach. One problem here could be that there might be a river where city A at the mouth of river has a fine treatment facility and city B 10 miles upstream does not.

3. The beach is a public asset that is managed by the state for the benefit of the state, and therefore the state taxpayers should bear the cost. This means, for example, that residents of Northern CA will be paying for sewage treatment for beaches in Southern CA.

4. Those responsible for the pollution should pay the cost to stop the pollution "at the source", so to speak.

Do you mean the pollution that people bring, or companies that are pumping their waste into the water? because if the state is going to bear the cost, everyone will bear the cost, people pay taxes to the state