I paddled for years in the Annapolis River in Nova Scotia, which ran right through the heart of extensive farming land, and was full of pollution. For many years, people weren't even supposed to engage in any water activities on the river. Likewise, my first wife's parents had a cottage on the upper reaches of the St. John River, in the heart of agricultural land….lots of pesticides and baddies in the water. I never experienced any hull degradation in any of the boats or canoes we used, including, but not limited to aluminium, fiberglass and wood.
UV rays from the sun, on the other hand, will damage many different types of hulls, so keep them stored out of the sun.