ST. LOUIS (AP) — The nation’s rivers and streams remain stubbornly polluted with nutrients that contaminate drinking water and fuel a gigantic dead zone for aquatic life in the Gulf of Mexico, according to a recently released Environmental Protection Agency assessment.

It’s a difficult problem that’s concentrated in agricultural regions that drain into the Mississippi River. More than half of the basin’s miles of rivers and streams were in poor condition for nitrogen and phosphorus from fertilizer that drains into waterways, the agency found. For decades, federal and state officials have struggled to control farm runoff, the biggest source of nutrient pollution that is not typically federally regulated.

It’s a problem only expected to get harder to control as climate change produces more intense storms that dump rain on the Midwest and South. Those heavy rains flood farm fields, pick up commercial fertilizers and carry them into nearby rivers.

“Controlling pollution is a big job. It is hard work,” said Tom Wall, director of watershed restoration, assessment and protection division at EPA. “Things are not getting worse, despite the tremendous pressures on our waterways. And we would like to see more progress.”

Water pollution from factories and industry is typically federally regulated. The Biden administration recently proposed toughening regulations on meat and poultry processing plants to reduce pollution, Wall said.

That affects the productivity of commercial fisheries and marine life in general, but nutrient pollution is also damaging upstream. Too much nitrate in drinking water can affect how blood carries oxygen, causing human health problems like headaches, nausea and abdominal cramps. It can especially affect infants, sometimes inducing “blue baby syndrome,” which causes the skin to take on a bluish hue.

The EPA established the hypoxia task force in the late 1990s to reduce nutrient pollution and shrink the dead zone, but it relies on voluntary efforts to reduce farm runoff and hasn’t significantly reduced the dead zone.

Anne Schechinger, Midwest director with the Environmental Working Group, said new regulations are needed, not voluntary efforts. She said the Biden administration has done a lot to improve drinking water, but not enough to reduce agricultural runoff.

Methods to prevent runoff include building buffers between farmland and waterways, creating new wetlands to filter pollutants and applying less fertilizer.

Martin Larsen, a farmer and conservation technician in southeast Minnesota, said he and other farmers are interested in practices that reduce their nutrient pollution. He’s broken up his typical corn and soybean rotation with oats and medium red clover, the latter a kind of plant that can increase nitrogen levels in the soil naturally. He’s been able to get by with about half as much fertilizer for a corn crop that follows a clover planting as compared to a corn-corn rotation.

Growing oats and red clover as cover crops improves soil, too. But Larsen said it’s difficult for many farmers to plant them when they often rely on an immediate payback for anything they grow. Cover crops are planted on just 5.1% of harvested farmland, according to 2017 data from the U.S. Department of Agriculture.

He said that many farmers in his community acknowledge the need to do things differently. “But we also feel very trapped in the system,” he said.

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Walling reported from Chicago.

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