If you’ve taken a trip to one of the many coastlines in the U.S. or Caribbean over the past year, there’s a good chance you’ve seen evidence of algal bloom. Murky shores, water with a red tint and beaches blanketed in stinking seaweed are some of the forms that harmful algal bloom can take.

Algal blooms are more than just unsightly and putrid. Harmful algal blooms can kill sea life, hurt businesses and threaten humans.

“They do pose human health risk,” said Dr. Christopher Winslow, interim director of the Ohio Sea Grant College Program and the Ohio State University Stone Laboratory.

Last year, Toledo, Ohio residents were warned not to drink or use the city’s tap water because algae-related toxins were found at one of the city’s treatment plants, The Weather Channel reported. The toxins came from an algal bloom in Lake Erie, which also provides water to cities including Cleveland, Buffalo and Detroit.

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The tourism and fishing industries are also threatened by harmful algal blooms. Businesses and communities have gotten a taste of the dangers that they can pose. Now, the conditions are ripe for large algal blooms this year, which has scientists on alert.

Norway-based salmon farmer Marine Harvest NO:MHG announced last week that it would have to restructure its Chilean business due to a severe algal bloom that is expected to kill 3.7 million salmon. The company US:MHG will have to cut up to 500 jobs.

Commercial crab fishing and clamming in the Pacific Northwest was delayed in December 2015 after a “warm blob” created an algal bloom. That blob was responsible for “the largest toxic bloom ever recorded off the West Coast,” said The Weather Channel.

Last year, Caribbean beaches were awash in a brownish seaweed that, the Guardian said, attracted “biting sand fleas and [smelled] like rotten eggs.”

Just weeks ago, the Phnom Penh Post reported that the government had advised people to refrain from swimming or eating fish in Kep, a Cambodian resort town known for its seafood, because of a large algal bloom.

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In September 2015, The Sentinel-2A satellite captured this image of an algal bloom in the Baltic Sea. A boat can be seen cutting a path through the bloom. Copernicus Sentinel data (2015)/ESA

Algal blooms, an overgrowth of algae in a body of water, are naturally occurring organisms. Harmful algal blooms, known by many names including red tides, blue-green algae, or cyanobacteria, can be toxic, according to the U.S. Environmental Protection Agency. They have become so prevalent in the U.S. that the government reauthorized the Harmful Algal Bloom and Hypoxia Research and Control Act in June 2014.

In February 2016, a 90-plus page government report about harmful algal blooms contained a number of recommendations, among them, “improve predictive capabilities by developing and enhancing harmful algal bloom and hypoxia model programs; improve disease surveillance for human and animal exposure, illnesses and death.”

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Algal blooms are caused by a mix of sunlight and warmth, slow-moving water and nutrients. Nutrient pollution can exacerbate algal blooms, making them more severe and more frequent.

Scientists MarketWatch spoke with tied these severe blooms to the warmer temperatures we’re experiencing: “It is related to climate change,” said Winslow.

Experts also say the extreme algal bloom activity is indicative of unhealthy waters. One of the things hurting waters is agricultural runoff.

Children swim in a “green tide” along China’s coastline in 2011. Getty Images

“Phosphorus is a major driver, and that source is likely fertilizers, whether chemical or manure,” said Winslow.

Winslow estimates that up to 85% of phosphorus runoff in Lake Erie is from farming. Other contributors are lawn fertilizers, failing septic tanks and sewer runoff. But overwhelmingly, said Winslow, agriculture is to blame.

“The heavy lift will be for farmers,” said Winslow. “I’m not blaming agriculture, but they have to change their practices. We have to keep the agricultural industry in Ohio vibrant, but at the same time address the algal bloom issue.”

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Ohio state tourism generates $40 billion, with $13 billion generated by the 88 counties on Lake Erie. Winslow lists the vast number of business areas affected by algal bloom, including charter boats that take fishing trips on the lake, hotels, small bait stores and more.

Over the last four years, 90% to 95% of the projects the Ohio Sea Grant College Program funds are focused on harmful algal bloom, totaling $2 million.

Lake Erie had its largest bloom last year. It was also the wettest June on record, with the number of storms as well as the amount of rainfall increasing.

So far, rainfall has been about normal for March and April, said Winslow. May, June and July, the three months that determine an algal bloom, are still up in the air.

Aquaculture, the breeding, rearing and harvesting of plants and animals in the water, as defined by the National Oceanic and Atmospheric Administration, is another practice believed to be driving large algal blooms. Adding food to feed a farm of fish and the excrement they produce “might just be one more factor that determines whether natural-born algae becomes a bloom,” said Thomas Bigford, policy director at the American Fisheries Society.

On the West Coast, experts are also trying to forecast this year’s algal bloom.

“We have people out on boats to see if we’re going to get something like last year,” said Dr. Raphael Kudela, chair of ocean health at the University of California at Santa Cruz.

There have been periods in history where environmental conditions deteriorate then bounce back. The oceans, for example, have seen big changes over millions of years.

But we may now be approaching a tipping point, where our waters and the creatures living in them can’t adapt. Bigger and more severe blooms aren’t going away anytime time soon.

“We’ve been lucky that the ocean is as resilient as it is, but if we keep pushing it, the ocean just will not recover,” said Kudela. “As time goes on, we’re seeing more and more evidence of bad things happening in the ocean.”

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