Not clear whether this has just occured recently or that you've noticed worsening hearing over a few years. If it's a recent observation you may try ear drops. I've had tinnitus a few times and it was remedied with drying out the ear canal using commerically available drops.
My experience with ear plugs was not good as my secondary response to the tinnitus was earplugs and what happened is that I'd developed 'swimmers ear' two times. I'd since learned that the skin in your ear canal is a bit unique and the ear canal is highly susceptible to infection if that lining is damaged. In my case earplugs chaffed that skin and made infection more possibe which led to the infections. I've since stopped using plugs and have been fine.
If drops don't help with the tinnitus relatively soon I'd see a specialist as it may be un-related to swimming.