When it rains in the Midwest, runoff from fertilizers laced with nitrogen and phosphorus leak into streams and creeks, many of them eventually dumping into the Mississippi River. The chemicals float hundreds of miles south into the Gulf of Mexico, then out to sea where they begin to spur algae and microbe growth.

As the algae decomposes, oxygen disappears. The water starts to suffocate. They become low-oxygen areas, often called “dead zones.”

Dead zones have increased more than 10-fold since 1950, according to a paper published in January by an international group of scientists for the Smithsonian Environmental Research Center. Last year, the Gulf of Mexico dead zone was the largest ever measured—about the size of New Jersey. As global temperatures continue to rise, dead zones in the world’s oceans, as well as in major U.S. waterways like the Great Lakes and Chesapeake Bay, are only expected to grow.

But many pollution sources that contribute to this growing problem, particularly the powerful agriculture industry, aren’t strictly regulated or held accountable for the role they play. Most states and the federal government have hardly begun to address the issue.

“The dead zone has been a frustrating thing to work on,” Matt Rota, senior policy director for the Gulf Restoration Network, told The Daily Beast. “It’s such a big problem and there are so many ways for people to point fingers.”

Agricultural runoff is the main culprit, but dead zones in the Gulf, along the U.S. coasts, and in the Chesapeake Bay are caused by a host of pollution sources, including discharge from sewage treatment plants and air pollution from vehicles. Combined, it creates a multitude of ecological consequences.

Animals move away from the low-oxygen areas so the only things left are microbes and small worms tolerant to warmer, hypoxic, or oxygen-deprived, waters. That leads to lower biodiversity in the open ocean and estuaries, shifting food chains, and habitat compression, said Lisa Levin, a researcher at the Scripps Institution of Oceanography who worked on the recent paper. Species like tuna and sailfish are forced to move towards the surface or around the dead zone, where they are caught by fishermen more easily.

Climate change is causing coastal dead zones to get worse, Levin said, making them“last longer, get bigger, and start earlier.” Unpredictable rates of precipitation mean more loads of runoff can occur in the spring, after farms are often fertilized.

Marine life isn’t the only thing at risk when this happens—coastal and inland communities within these major watersheds feel the effects, too. Toxic algal blooms can break out on the surface of hypoxic waters, costing coastal towns millions of dollars in cleanup while harming the tourism, fishing, and outdoor recreation industries. Fishermen catch smaller shrimp, which can lower their price and affect the Gulf’s billion-dollar seafood industry that sustains the regional economy.

Nitrogen and phosphorus pollution impacts other water sources also, including wells, lakes, and streams that provide drinking water far from the coasts. High levels of nitrates from fertilizers found in Iowa’s water supply, for instance, have been linked to birth defects such as “blue baby syndrome,” certain types of cancers, and thyroid problems.

Don Scavia is a University of Michigan professor who had a 30-year career in NOAA, where he helped launch the first major assessment of hypoxia in the Gulf of Mexico. He said it showed the U.S. would have to “reduce the [nutrient] load in the Mississippi by 35 or 40 percent.”

The EPA has encouraged Midwestern farmers to stop nutrients from running off by planting strips of grass or forests to trap fertilizer or not spraying when the ground is still frozen.

But nothing is mandatory.

“Here we are 17 years later, and the load hasn’t changed,” Scavia pointed out. “Whatever they’ve been doing in the Mississippi Basin to control those loads has not been effective… we haven’t done enough of what needs to be done.”

Hope in the Chesapeake Bay

After many years trying to get farmers to voluntarily reduce nitrogen and phosphorus pollution in the Chesapeake Bay, the EPA established a Total Maximum Daily Load (TMDL) in 2010 that sets a cap on nitrogen, phosphorus, and sediment released into the six-state watershed each year that is supposed to help restore Bay and its tidal rivers by 2025. The 2008 Farm Bill also had a specific component that addressed pollution reduction efforts in the Chesapeake Bay watershed and helped farmers fund changes to their farming practices.

Those initiatives worked: Over time, the dead zone has gotten significantly smaller, Beth McGee, director of science and agricultural policy for the Chesapeake Bay Foundation. “We need to keep doing it,” McGee said. “We’re clearly not out of the woods yet, but the fact that what we’re doing is showing improvement is astonishing.”

The Chesapeake Bay watershed is much smaller than the Gulf’s, and some of the states that contribute the most pollution also directly benefit from the water, McGee added. “There’s a lot of bipartisan political support for bay and wanting to get it cleaned up,” she said.

“ In the two-year policy cycle this country works on, it’s hard to get people to bite the bullet when they can’t see the results. ” — Don Scavia, University of Michigan

That’s partially why tackling pollution plaguing the Gulf watershed is much more complicated, experts say—the Midwestern states contributing the most harm to the ocean are far removed from it and don’t have much incentive to do so.

Under the Trump administration, it’s unlikely that the EPA will crack down on pollution from farming operations, environmental advocates and experts say. The agriculture industry is largely exempt from the Clean Water Act. Last year, EPA chief Scott Pruitt released a proposal to repeal the 2015 Waters of the United States rule, which updated the Clean Water Act to define what waterways can be regulated by the federal government The agriculture industry has lobbied hard against the rule, arguing that it is federal overreach and makes it difficult to discern which ditches, drains or low-lying areas on their property would be under federal jurisdiction.

Aside from massive shifts like reducing carbon emissions and mandating caps on nutrient runoff, there are smaller-scale solutions, like fishing less tolerant species and putting more energy into fishing climate change-tolerant ones, Levin said. The Gulf Restoration Network is also pushing initiatives to get major agriculture companies like Tyson to source fertilizer-free corn and soy for their animal feed.

But all that depends on state and local government agencies to cap nitrogen, phosphorus, and sediment. “I don’t see a silver bullet,” Scavia said. “It’s going to take a long time before you see a change in the load, and in the two-year policy cycle this country works on, it’s hard to get people to bite the bullet when they can’t see the results.”