If you look at the photo above and ignore the guy sitting on the rock, you will see how clear Tahoe water is.
Unfortunately, Tahoe has been getting less clear for years. Silt in runoff and pollution have been considered to be the main culprits.
In a counter-intuitive way, more snow and its resulting melt waters have not seemed to aide clarity. It had been thought that more runoff meant more silt.
However, starting last fall, the lake has gotten unexpectedly clearer. The scientists at UC Davis who have studied Tahoe clarity for the last sixty years weren't sure why. They've come up with some answers, which are detailed in the Lake Tahoe Clarity report:
https://tahoe.ucdavis.edu/secchi
They think we've had a sudden population boom of a particular zooplankton that eat clarity-robbing algae. Why? Because of a sudden population bust of a particular tiny shrimp that eat the zooplankton. Why have the shrimp's numbers collapsed? From what I've read, they don't really know.
The helpful zooplanton have the lovely names Daphnia and Bosmina. Here's a pic of a zooplankton after feasting on a chunk of green algae.
Daphnia plankton are little, a millimeter or two long, which means their length is about the same as the thickness of a paper clip wire. Think of them as tiny little water vacuums, keeping our lake clear.
The offending shrimp are called Mysis shrimp. And, naturally, they are not native to Tahoe but were introduced by people back in the '60s.
Mysis shrimp are much bigger than Daphnia plankton. Their length ranges from a quarter inch up to one inch. Still small, but probably terrifying if you are a Daphnia plankton!
When Mysis shrimp eat all the plankton, the algae population goes up, and lake clarity suffers.
The Earth's ecosystems are complex and interconnected. No doubt, the shrimp population will rebound and lake clarity will once again diminish. Let's hope that takes a long time.
