Fortunately, for U.S. mariners a great number of the waterways that used to be open sewer that cities and towns just dumped their wastewater into indescriminately, have been cleaned up thanks to massive infusion of local and state funds, matched by massive federal funding.
One local river we know about, the Charles in Boston, has moved up in water quality from open cesspool quality to B+ or swimmable again thanks to efforts of the many communities along the urban river that actually rises about 30 miles south and west of the city.
Towns and cities that used to dump their sewage and rainwater directly into the Charles are now using pumping stations or putting the wastewater into the pumphouse at Deer Island where it undergoes further cleaning and after a ride through a 300-foot deep aeration/filteration system, the water emerges clean in the middle of Massachusetts Bay clean.
For the boat owner who uses the Charles this is great news because it means that you really don't have to clean the old boat up fitting by fitting to ensure that pollutants and other detririus (Huggies and their spawn have been known to float in the same water and Environmental Police officers, thanks to the cleaner water, have been able to track down the offenders and given them back their "presents" along with "presents" from the state in the form of court summonses.
In the old days, we were told by an old aluminum boat owner, he had to hose down not only each rivet in his riveted boat, but also each panel and then run the engine in a clean barrel of water to get the gunk out. Now you no longer have to do that (although it really doesn't hurt once in a while).
Indeed, he found that the rivets in his aluminum 15-footer were constantly pounding free and he spent many of his trips bailing out the his aluminum runabout. He was never more happy than to get rid of the riveted boat and pick up a welded one.