In the News

Tahoe’s Dogs Make an Impact on Lake Water Quality
date posted: May 18 2004

By John Cobourn, Water Resource Specialist; and
Heather Segale, Environmental Education Coordinator; University of Nevada Cooperative Extension

If you have been reading our weekly articles, you know there are plenty of things we can do to help protect Lake Tahoe. Perhaps one of the less obvious remedies is to pick up after our dogs. Our dogs and other pets make a significant impact on Tahoe’s water quality.

Dog feces and urine contain relatively large amounts of nitrogen and phosphorus, the nutrients that feed and stimulate the growth of algae in the lake. In addition, bacterial contamination from the feces affects recreational uses of streams and can even affect the drinking water taken from Lake Tahoe.

How many dogs are we talking about? According to the animal control offices in Placer and El Dorado counties, 5,200 dogs were licensed in the California portion of the Tahoe Basin in 2003. If we estimate that there are another 2,000 licensed dogs in the Nevada portion of the basin, and that approximately half of the dogs in the basin are licensed, a rough estimate of Tahoe’s dog population is 15,000!

Bruce Warden, a scientist at the Lahontan Regional Water Quality Control Board, analyzed the nutrient content of dog food. He assumed that, except for puppies, the amount of nutrients going into dogs is about the same as that in the dog waste. He then estimated that an average weight of Tahoe dogs as 45 pounds. From this information, he calculated an average deposition of 13 pounds of nitrogen and 2 pounds of phosphorus per year per dog. That’s about 90 tons of nitrogen and 15 tons of phosphorus per year. A high percentage of the nutrients are in a chemical form that is readily used by algae as food.

The problem with dog waste is that it doesn’t normally go into sanitary sewers to be treated and exported out of the basin the way human waste does. For this reason, pet owners are urged to take along a plastic bag when walking their animals and to dispose of feces in a trash receptacle or down the toilet.

This is a matter of public health as well as the lake’s water quality. If humans step in dog waste and track it into the house, children can get it on their hands and run the risk of infection from fecal coliform bacteria. Moreover, pet waste can carry two troublesome parasites, Giardia and Cryptosporidium. Children are also especially vulnerable to these disease-causing organisms. If either parasites or bacteria enter the lake, they can end up in the drinking water in communities that take their water, unfiltered, from the lake.

It is generally more important to pick up after our pets on trails, near streams and lakes, or anywhere that pet waste could be flushed into storm drainage systems, which normally discharge to the lake. Since people usually like to walk their dogs in such areas, owners should make it a normal routine to pick up after their pets.


What about geese?
You might have noticed that Canada geese are now year-round residents of the Tahoe Basin. These handsome birds ingest phosphorous and nitrogen when feeding on grasses that have been fertilized. They then deposit droppings on our lawns, beaches and elsewhere. The effect of this waste is different from that of dogs, however. Julie Regan, TRPA, points out that geese are ingesting nutrients that already exist around the lake. The geese are basically recycling the fertilizer they’re eating from the grass. Dog waste can actually add to the overall pollution of the lake because their food source is over and above what is in the environment.

Canada geese now live here in large numbers partly because we have created year-round habitat in the form of large fertilized turf areas. Some scientists think that if we reduce the acreage of fertilized lawns, a food source for geese, we could limit goose populations. In the meantime, you can encourage beach patrols and neighborhood groups to be aware of goose waste near beaches and streams.


Watch for “The Lake Tahoe Report” in the North Lake Bonanza each Friday, and tune in to KOLO-TV News Channel 8 Tuesdays at 5 p.m. to learn more. “The Lake Tahoe Report” is a collaborative effort of the Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis and the USDA Forest Service. For more information, contact Heather Segale, University of Nevada Cooperative Extension, (775) 832-4138, or logon to www.lteec.org or www.unce.unr.edu.