This is always a fun topic. As far as the lead ban, I'm pretty sure its all about the waterfowl. The following site has some interesting stuff at the end about loon deaths due to lead toxicosis.
http://www.tufts.edu/vet/loons/index.html
As far a water pollution, remember a couple of decades ago when you heard a lot about acid rain. Well the clean air act of 1990 along with a host of technological advances have really squashed this. The reason that the northeast suffered from acid rain wasnt because of powerplants/factories in this area as much as those in Ohio, Illinois, Pennyslvania, etc. In those states it became common practice to build your smoke stack crazy high which sends SOx and NOx into the atmosphere where the jet streams catches it and delivers all the "goods" to new england. Fortunately things have changed and water quality has greatly improved.
As for the mercury/pesticides/etc in the lakes that result in MA posting a fish advisory, this can definitley be attributed to unregulated companies abusing the local bodies of water (mercury is also contained in coal exhaust). Did they actually go pour gallons of mercury into the lakes? No but waste from companies that use mercury containing devices (medical community/neon lights) if not properly disposed of gets buried at your local landfill and subsequently into your water. Regulation along with testing/monitoring over the last many decades has definetly helped this.