
San Diego County has 12 water reservoirs, and they are all now officially infiltrated by the quagga mussel. A tiny fresh-water mussel, the quagga is a close relative of the infamous zebra mussel, which has caused millions of dollars of property damage in the Great Lakes. The city is working on eradication, but don’t count on it - this little dudes are nearly impossible to remove once they’re established.
These tiny mussels wreak havoc in two ways - filtering the water and clogging pipes and walls. By removing tiny plants and animals from the water, the mussels take away food from native critters, fertilize the bottom with their excretions, and allow more light to reach deeper in the lake. This creates perfect conditions for invasive and/or noxious plants to take over the bottom of the reservoir. And mussels love high water flow, since it brings more food their way - which means that their favorite places to live are in intake pipes.
Unfortunately, they are going to be very hard to eradicate. Mussels are broadcast spawners, which means that each individual can spooge out millions and millions of sperm or eggs into the water. As long as there’s one male and one female and they are close enough together to fertilize, millions and millions of baby mussels can be pumped into the lake. And the larvae are hardy - a mussel larvae floats about for about four weeks before settling to the bottom and becoming an adult mussel, plenty of time to be sucked into a boat’s ballast water and transported to another lake.
Because of this decandent molluscan lifestyle, the city’s proposed solutions are a bit laughable. Lowering the level of the reservoir, pulling adults of lines and floats,. dredging the lake - none of these will address the problem of a month’s worth of microscopic larvae just waiting to turn into brand new adults. Unless there is a way to simultaneously remove all adults, then do it again in a month when the larvae settle, then do it again to clean up any stragglers - but such a way would likely kill everything in the lake. It seems likely that the quagga mussel is here to stay - too bad they probably don’t taste good with coconut-basil sauce.
Further info: Here’s a comprehensive FAQ from USGS