Green Storms in Blue Water: Unexplained Algae Blooms Increasing in Freshwater Lakes

Something troubling is happening in freshwater lakes around the world—algae are acting decidedly peculiar. On pebble-strewn waterfronts at Lake Tahoe, California, along sandy shallows in Ma¯ori Lake, New Zealand, beneath layers of cold, clear water in Lake Baikal, Russia—even at Bear Lake in northern Utah—long strands of slimy green algae are mustering explosive growth and hijacking ecosystems. It’s a phenomenon that’s particularly alarming to researchers, as the algal blooms can’t readily be predicted by established successional patterns, according to a newly published overview from Soren Brothers, ecologist in Utah State University’s Ecology Center and Department of Watershed Sciences in the S.J. & Jessie E. Quinney College of Natural Resources, and others.

Occasional invasions of algae aren’t all that unusual—they are often a sign of high levels of phosphorus and nitrogen in the water from pollution sources. But these new blooms are appearing in lakes that don’t experience much human impact from pollution or recreation, and don’t have any of the normal warning indicators. Neither are the blooms caused by invasive species of algae; the aggressive algae are often the same types that have quietly resided on lake bottoms for decades.

Very clear lakes usually boast high water quality. A combination of sunlight and clean water means that algae residing in these lakes remain low growing and relatively inconspicuous, providing a foundation for much of the natural food web that occurs in the lake. But these new blooms aren’t following the same pattern. Algae are forming dense carpets across clear lake bottoms or stretching surfaceward in towering columns, with amorphous clouds of stringy green fingers filling vast areas, seemingly out of the blue.

So what happens when a foundation of your ecosystem goes, for lack of a better term, berserk? It’s likely a major structural and functional shift for lake ecosystems, said Brothers. Piles of algae can be washed ashore creating windrows of rotting algae that clog fishing nets, harbor toxins, and accumulate harmful bacteria. We have yet to know the full extent of how these filamentous blooms are affecting ecosystems, according to Brothers.

Researchers are investigating why the algae blooms are occurring, but have only well-investigated speculation at this point. For instance, it could be that pollution is infiltrating lakes—not through over-ground streams and rivers, but in groundwater, feeding algae from the bottom up. Or it could be that the changing climate is creating a warm zone of stratified water that prolongs the algae’s growing season. Or perhaps that there has been an unrecognized drop in a limiting factor in the ecosystem, such as populations of lake-dwelling herbivores like mayfly larvae.

More work is needed to get to the bottom of the mystery, but the authors say it’s essential and urgent that we begin to look for answers. Their recommendations include establishing criteria that allow the public and scientists to identify the atypical algae blooms and report their occurrence, to standardize methods for monitoring attached algae blooms, and incorporating these methods into existing lake monitoring programs.