The Importance of Watersheds: A Lake Tahoe Story

The Importance of Watersheds: A Lake Tahoe Story

California’s Lake Tahoe is renowned the world over for the clarity of its water, a clarity that has enabled the viewer to see a Secchi disc 120 feet down.  But over the decades, that lake has shown decline.  Tahoe’s story is a lesson we need to learn.

Researchers have noticed that when development around the lake began decades ago, the water clarity had been reduced by nearly one foot per year since.

Extensive scientific studies over the years have gathered considerable amounts of data on the lake and its condition.  Their conclusions are sobering.  Get this: Eighty percent of the loss of clarity in the lake is due to fine sediments from urban storm water.

What happens at the shore has a huge impact on lake water quality.  But what happens in the watershed is equally important.  Research reveals that in the Tahoe area, events in the watershed caused 80 percent of the lake’s decline in water clarity.  A watershed.  Recall what a watershed is: all the land that is drained by a stream or river.

That problem plagues lakes everywhere.

What sorts of materials get into urban storm water that can degrade lakes?  Nutrients, fertilizer from lawns, bacteria, sediment particles, heavy metals, oil drips from cars, excessive salt, and leaves getting into storm water pipes and basins are examples.

Part of the problem is that we have so much impervious surface in our communities—driveways, roofs and other surfaces that prevent water from soaking into soil.  Instead, water rushes rapidly on those impervious surfaces carrying with them all manner of unwanted materials.

Reducing urban storm water runoff can be expensive without home owners pitching in. Individuals can help protect lakes from urban runoff: establish a simple rain garden, dispose of toxic materials properly, spare the lawn fertilizer.

Details about Lake Tahoe came from the Michigan Riparan, a magazine for lake activists.

Darby Nelson

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