Climate change isn’t just raising temperatures — it’s also changing precipitation patterns around the world.

In the decades ahead, some places are at increased risk for drought, while others can expect more rainfall.

At first glance, drought might seem like the worse scenario. But more rain comes with hazards as well, including more industrial and agricultural runoff.

Read More: 6 of the Hottest Places in the World, With or Without Climate Change

But according to a new story, too much rain will also have deadly outcomes.

A new study in the journal Science argues that as rain increases in agricultural and industrial zones in the US, nitrogen runoff could increase by 19%, which would promote the growth of a toxic algae, rendering many water sources essentially unusable.   

As rain floods farmland more often, more nitrogen-based fertilizer will be pulled from the soil and carried to waterways.  

The eventual toxic algae blooms that occur can kill fish by depriving water of oxygen; make shellfish dangerous to eat; make the surrounding air hard to breathe; and make water too contaminated to drink, according to the National Ocean Service.

Warming temperatures on a global scale will also spur the growth of this toxic algae.  

“In reality, what happens to water quality is more about this interplay between what we as humans are doing locally — things like land use and land management — and what we as humans are doing globally, in terms of climate change,” Anna Michalak, an earth scientist at the Carnegie Institution for Science and a co-author of the report, told The Washington Post.

Read More:  Turns Out There’s Not Just 1 Great Oceanic Garbage Patch — There Are 5

Some of the most vulnerable bodies of water in the US will be the Great Lakes and the Gulf of Mexico, according to the study.

The authors looked at three different future scenarios — if global emissions remained constant, if they were partly reduced, and if they were substantially reduced.

All three scenarios saw an increase in nitrogen pollution, but the constant scenario was the most extreme.

The authors noted, however, that nitrogen use could fall off in the years ahead as more efficient farming methods are discovered, which would lead to less pollution. At the same time, nitrogen use could become even more intense, which would lead to even havier pollution.

Toxic algae blooms are a problem around the world, especially in areas of high industrial activity where runoff is common.  

The third largest lake in China, Lake Taihu, provides water to more than 30 million people, but an algae bloom has nearly taken it over.

Read More: These Are the 5 Deadliest Countries for Environmental Activists

In the US, officials in Ohio barred Lake Erie from being used for drinking water when an algae bloom grew out of control. The Gulf of Mexico, meanwhile, has a huge dead zone from runoff that travels down the Mississippi River.

The problem is more far-ranging than this. Every state in the US faces nutrient pollution in their water sources, according to the EPA.  

The consequences of climate change sometimes seem abstract — melting icebergs, ocean acidification, broader ranges for dangerous pests — but drinking water is far from abstract.

The authors of the report ultimately hope that measures are taken to both reduce nitrogen use and limit emissions so that worst case scenarios can be avoided.

“There is potentially an exciting optimistic story to be told about global nitrogen stewardship in the Anthropocene,” they concluded their report.