Copper sulfate is an inorganic compound that combines sulfur with copper. It can kill bacteria, algae, roots, plants, snails, and fungi. Many local farm stores keep the product on store shelves helping to make it the most used, and the most economical algae control available for ponds and lakes. Copper Sulfate is ineffective in the long term unless combined with other management methods. Both filamentous and planktonic algae can grow back quickly following herbicide applications.
Copper is a heavy metal and when it is applied to water it will sink to the bottom and accumulate in the sediment rather than staying suspended in the water column. The accumulation of copper sulfate after application can create a sterile water bottom where important nutrients and bacteria that fish and other aquatic life need are killed off. Copper sulfate can weaken the aquatic food chain by killing off weaker fish who need the nutrients to survive, this leads to overpopulation of some species for short periods of time (until they die off because they are without a food source). It also creates over-oxygenated water which can also cause plants to die. Lastly, animals that drink from this water may be at increased risk of injury or death.
A long-term study of lakes in the Fairmont Chain of Lakes in southern Minnesota has demonstrated that the lake bottom is almost devoid of life, and that the algae blooms that were the impetus for treating the lakes in the first place, have become worse over time, in spite of being treated with copper sulfate every year. The lakes have effectively become biological deserts.