unless you have a hole in the ear drum, water in the ear canals may lead to muffled hearing, but not to ongoing hearing loss or tinnitus.
What is the proposed mechanism that swimming can lead to tinnitus?
I have had tinnitus as long as I can remember. It's worse if I stay up too late, or if I am in loud environments. I've always had very sensitive hearing...hyperacousis...and don't like loud noises or environments. If the ear canal is filled with water, the signals that normally help my brain filter out the tinnitus are no longer there and it can make it more prominent.
But it's certainly not a cause and effect. It's there and sometimes it's worse...but not caused by the water.