Industrial and municipal pollutants. While agriculture remains the biggest source of water pollution, wastes from industries and municipalities have increased enormously in recent decades. Industrial pollutants, such as wastes from chemical plants, are often dumped directly into waterways. Oils and salts are washed off city streets. Furthermore, pollutants such as sulfur dioxide and oxides of nitrogen, which combine in the atmosphere to form acid rain, have had pervasive effects on both freshwater and land ecosystems.
Acid rain lowers the pH of rivers and streams.
Some of the worst pollutants are synthetic chemicals. Many of them find their way into rivers, lakes, and groundwater aquifers. They do not break down easily under natural processes and thus tend to accumulate up the biological food chain, until they pose risks to human health. Indigenous communities that once hunted these whales no longer are permitted to take any because of the health risks.