MAJOR CAUSES OF WATER POLLUTION Water pollution comes from a variety of point and non-point sources. In the 1960s and 1970s, the leading contributor of nutrients that caused algal blooms was point source pollution from the release of sewage treatment plant wastewater, a pollution source that was effectively addressed. The new round of algal blooms that began in the 1990s is likely due to nutrients from non-point sources, although point sources still play a role.