9 Invasive Species Costing US Water Systems Millions
By Walt Kesler, Power plant maintenance manager, nuclear-qualified. Reviewed by Amanda McCallister, editor.
Environmental Diving | Cathodic Protection & Anodes October 2017. Red Wing, Minnesota. I was standing on the intake deck of a small coal plant, and the traveling screen was so caked with zebra mussels the drive chain had snapped. It was 3 a.m., we had one unit at half load, and the city was just waking up. My supervisor handed me a pressure washer and said, 'Make it clean.' I didn't know then that we'd spend the next decade chasing invasive species — and that they'd cost us more than any gasket or bearing failure ever did. That night I learned the first rule of intake screens: you don't fight a biofouling problem; you manage it. Mussels, plants, fish, and even a crustacean the size of a paperclip can shut down a circulating water system faster than any pump failure. This post is the shortlist of the nine that cost US water systems real money, and how we handle them.
The Bivalves That Shut You Down
Zebra mussel (#1). The original troublemaker. It attaches to any hard surface inside your intake pipe, condenser tubes, and screen mesh. The real cost isn't just cleaning — it's the microhabitat they create for their quagga cousins. We've had to grind through four-inch-thick layers on a trash rack. The fix: a combination of low-voltage electric fields, thermal backwash, and chemical treatment. You never get rid of them; you just keep the population below the point where it costs you a shutdown. Quagga mussel (#2). The zebra's darker, more persistent twin. They tolerate colder water and deeper depths, so they'll colonize the entire water column. At one plant, they got into the condenser tubes and we lost a measurable chunk of heat rate in a single season. The only effective way is continuous chlorination at the intake, but you have to balance that with discharge permits. So you're stuck with mechanical cleaning, and that's a labor bill that never ends. Asian clam (#3). The sleeper hit. They don't attach like the mussels — they burrow into the sediment and quickly multiply. They'll clog your low-pressure side and your fire water system. We found them in the strainers of an auxiliary cooling pump. The trick is to keep your intakes designed with high velocities so they can't settle, and to do seasonal flushing of the low-flow lines.
Plants That Choke Your Screens
Water hyacinth (#4). A floating plant that grows so fast it can double in area in about two weeks. It mats up against your intake screens, and the mat holds sediment and trash, which makes screening even worse. We've used a skimmer boat and a hydraulic raking system, but the real fix is a barrier boom upstream. You have to weed it every day in summer. Hydrilla (#5). This one's worse because it's submerged. It grows in up to 40 feet of water and can fill a canal until it looks like a green carpet. It wraps around rotating screens and jams the drive. We've had to install a vertical cutter in front of the intake, and even then we get partial clogs. It's a year-round battle in the South. Eurasian watermilfoil (#6). Similar to hydrilla, but it spreads by tiny fragments. One boat propeller can introduce it clear across a reservoir. It doesn't clog as badly as hydrilla, but it increases the sediment load on your screens. The answer is targeted benthic barriers over the weed beds nearest your intake, plus an aggressive monitoring program.
The Opportunists That Make Everything Worse
Spiny water flea (#7). Don't let the size fool you. It's a zooplankton with a long spine that collects in big clumps on a fine mesh. They'll blind a traveling screen in hours. Since they're plankton, there's no point in physical barriers — you need a backwash system that can reverse flow through the screen, and you need to count them in your raw water sampling. We've had days where we stopped all intakes to let screens backwash. Silver carp (#8). The jumping fish that's all over the news. They'll leap out of the water when a boat motor passes, but at a power plant, they jump up onto the intake deck when the current gets strong. It's not the fish themselves; it's that they pile up against the trash racks and create a mushy mass that blocks water. We've installed a fish deterrent (an air bubble curtain) upstream, and we still have to use a crane to pull carcasses off the screens. Phragmites (#9). The common reed. It doesn't grow in the water column, but it invades the shorelines and shallow areas. The problem is it escapes a managed wetland and starts clogging the open channel between your forebay and the circulating water pump. It also provides cover for rodents that eat electrical insulation. We control it with shoreline mowing and careful herbicide, but it's a constant push.
Frequently Asked Questions
Can't you just poison the intake with chlorine? You can, but you have to balance chlorine residual in the discharge. A continuous low dose works for mussels, but plants and fish need other methods. We use chlorine only as part of a broader strategy, and we monitor the hell out of it. Why not just put a bigger screen over the intake? A bigger screen just gives you a bigger cleaning problem. The invasive species grow on the screen itself. The real answer is integrated pest management: deterrents, regular cleaning, and chemical control calibrated to the species you're dealing with. Which one do you dread the most? Zebra and quagga mussels. They don't just clog the screens; they get inside the condenser tubes, eat away at your heat rate, and turn every shutdown into a scrap-out operation. The others you can see coming. The mussels you don't, until it's too late.