Something in the water?

I have been surfing/surf life saving for the last
Ten years of my life on the mid coast of south aus.
Bit of a downer topic but interesting. In the last 2 to 3
Years at least six people have been diagnosed with some
Form of cancer from my local surf club , another was just diagnosed yesterday.
Starting to get a bit sus as none of these
People would be considered 'old ' either or unhealthy(4 of these were two couples)and with dolphins
Washing up with fish every where on the mid.
Does any one know if it is possible something in the water
Could be doing this? And who looks into it? I have also heard
People say don't surf or swim two days after rain on the mid too..