Why is mercury in fish on the rise?

Likely pollutants.: Because of the chemical wastes dumped into rivers and lakes, etc. For many decades, there is more mercury in fish. Also, there are many more fishing vessels catching more fish in the world, so there is more exposure to mercury. Still anotyer reason is due to fish at the top of the food chain eating others and concentrating mercury in them.

Pollutants: More than likely it is due to pollution of the water supply.