Several lakes, rivers and coastlines around the United States are choked with green muck.
The cause are giant clouds of algae — known formally as "harmful algal blooms" and they can shut down fisheries, dampen tourism, and cause serious health problems in humans and animals alike. They are, at root, a natural phemomenon, but scientists who study them say they have become more common and more severe in recent years.
An algal bloom blankets Lake Erie, and a bloom has spread around a lake in Utah, forcing officials to close it to visitors, according to the Salt Lake Tribune.
Recent news reports have also documented the algae bloom that has spread through Lake Okeechobee in Florida and clogged the waters around state's tourism-heavy coastline with the slime. Other blooms have been reported in Idaho, and in two lakes in California.
There are thousands of species of algae in the oceans, and at least hundreds in freshwater bodies. Of these multitudes, there are relatively few that are toxic, according to Donald Anderson, an algae researcher, who is director of the U.S. National Office for Harmful Algal Blooms at Woods Hole Oceanographic Institution.
Algae blooms have a variety of causes, and in many cases they are merely the result of natural changes in temperature or other environmental fluctuations.
The algal blooms that Anderson and his colleagues work on in the Gulf of Maine are almost entirely natural. However, in some cases, particularly in some freshwater blooms, humans are playing a part.
"There is no doubt that pollution is making things worse," in many cases, Anderson said.
One condition always necessary is some sort of food source for the algae, often nitrogen or phosphorous. Both are plentiful in fertilizers, and in sewage. The blooms in Lake Erie and Lake Okeechobee are being fed by fertilizers and other land pollution runoff. Utah Lake's bloom is being fed by treated wastewater that has been flowing into the lake, according to the Salt Lake Tribune.
About 140 people calling Utah Poison Control inquiring about the bloom reported having symptoms, ranging from gastrointestinal problems (nausea, vomiting, diarrhea), to headache, or irritated eyes or skin.
A changing climate is may also be having some impact, Anderson said.
"Some of these species are especially good competitors, especially in warm or hot conditions," Anderson said. "And again that holds for the species that you are hearing about on Lake Erie and down in Florida. So if you start having hotter summers with hotter waters they can start to start to really succeed over the other competition."
However, Anderson said it is too early to say that there is a single of common cause behind all the rise in algae blooms. These are different species in different environments. And some of these blooms are not new to 2016. Lake Erie has had large algal blooms for years, for example.
And the aforementioned bloom off the West Coast "was not a pollution story," Anderson noted.
So what can be done about the problem?
Managing pollution could be a start, but might require broad restrictions on chemicals. Much of the pollution does not have a single identifiable source — so restricting it would require very far-reaching restrictions on the use of chemicals.
"It is not like this is coming in from a single sewage treatment plant, where you can treat it very well," Anderson said. "It is coming in from everywhere."
"It is difficult to tell someone up Minnesota that what they are doing is affecting the Mississippi and the Gulf of Mexico, which is so far away," he added.
Developing forecasts is part of the effort to manage blooms. Forecasts would let institutions prepare for the events, at the very least. Researchers have been able develop various techniques for forecasting algae blooms, such as combining satellite imagery with computer simulations. They have been able to use satellite images of the Lake Erie bloom to determine how the bloom might spread, move, or shrink. But that requires the bloom to be visible in space.
Anderson and his colleagues also sample mud in the Gulf of Maine every fall and look for the algal organisms when they are in their dormant phase. "And that turns out to a be a hugely important indicator of how severe the next year is going to be," he said. "That kind of forecasting, seasonal forecasting, has for us been very accurate."
But algae bloom researchers lack the field instruments that would enable them to have the same kind of accuracy and texture as weather forecasts.
"We have the same physics, the same models, but what we don't have are the dense observations from weather stations everywhere," Anderson said. "It is a big push in our field, a big push in oceanography in general to be instrumenting the ocean much, much more, so that we can do that kind of forecasting."
Another solution that has worked elsewhere in the world is spraying clay on affected areas. Clay is a natural substance — it doesn't pollute — and works by dragging the algae down to the bottom of a body of water, and essentially destroying or burying it.
But dumping or spraying compounds to kill off a cloud of algae moving through the water is far more difficult than spraying a field of vegetables, Anderson said. There are strategies available but they could use more research. And environmental restrictions have made it harder to adopt in the United States.
However, Anderson said the field needs more funding. Even as the problem grows, the amount of federal money available for harmful algal bloom research has been cut.
"We are running on fumes," Anderson said. Years ago, there was about $22 million of government funding available to the community of scientists who study blooms. Now, it is more like $9 million, he said.