Freshwater fish are always a concern for parasites. In the US, sushi chefs freeze the salmon for one week to kill any parasites or eggs. If the fish you are eating raw is properly prepped, parasites are not a problem.

Undercooked salmon is another issue altogether. Since it is not prepped to be eaten raw, undercooking is very dangerous. Those fish meant to be eaten raw (anything in a sushi bar) are prepped with parasites in mind. Even tuna, which is a deep water ocean fish, is often frozen before being served 'fresh' and raw.

If you go to a good sushi restaurant, parasites will not be a problem. You are at a far greater risk eating undercooked beef and chicken at a western restaurant.