Pesticides and Water Quality

A 1999 study on "The Quality of Our Nation's Waters" found that insecticides are detected more often, and usually in higher concentrations, in urban streams as opposed to agricultural streams. Most commonly found were diazinon, carbaryl (sevin), and malathion. Diazinon was commonly used by homeowners across the country until an agreement between EPA and product registrants resulted in its removal from retail store shelves (over-the-counter products) after December 2004. The agreement also resulted in the removal of dursban (chlorpyrifos) from store shelves in December 2001 because of health risks to children. Though malathion and carbaryl are less toxic than diazinon, they are more water soluble -- meaning they wash off lawns and streets a lot more easily so more of it gets into our waterways.

It doesn't take much of some pesticides to affect wildlife and water quality. 

Consider this:

DuckJust one granule or seed treated with diazinon is enough to kill a small bird!  And, the equivalent of 1 drop of diazinon in two backyard swimming pools is enough to kill the  "water flea," which is at the base of the food chain.


FrogBifenthrin - another common ingredient in some over-the-counter pesticides -  is toxic  to aquatic life at 4 parts per trillion.  That's like 4 square feet of tile on a kitchen floor the size of Indiana!


  • Carbaryl is toxic to aquatic life at 0.8 parts per million!   That's the equivalent of less than one inch in 16 miles; or, less than one ounce of sugar in 7,813 gallons of Kool-Aid!
  • Malathion is toxic to aquatic life at 340 parts per trillion. That's like 340 drops of detergent in enough dishwater to fill a string of railroad tank cars 10 miles long!

For more information on pesticides, refer to organizations listed in the Resources section of this website and the U.C. Davis water quality website. Also link to the Our Water - Our World fact sheet:  Pesticides and Water Quality.