What My School’s Toxic Lake Taught Me About Water Quality

How farm runoff is poisoning our water — and what we can do about it

Hidden in the Arcata Community Forest behind Cal Poly Humboldt’s Kinesiology and Athletics Building rests Fern Lake, a reservoir that supplies water to the school’s fish hatchery. On the surface, the lake looks fine. The water looks clear enough, the shoreline is green with vegetation, and on warm afternoons a turtle basks on the fallen trees. But last fall, something changed in Fern Lake’s water, and a lot of fish died because of it.

My water quality engineering class has been tasked with solving this fish-murder mystery. Every week, my classmates and I hike to Fern Lake carrying sampling bottles and begin collecting data. Some measurements, like temperature or pH, must be taken right there in the field because these parameters change the moment a sample leaves the water. Other tests are done back in the lab, where analysis could take hours or days. We test samples from the lake itself, the stream flowing in, and the outflow that feeds the hatchery to understand the water’s health from source to destination.

Going through this process taught me that the water quality of any lake, stream, or river is inseparable from the land around it. And when that land is used the way most of American agriculture uses it, the water quality suffers, along with the people and ecosystems that use it.

Chemistry of a Crisis

To understand what’s happening in water bodies like Fern Lake, it helps to know what nitrogen and phosphorus actually do. And why too much of them can be a problem.

Both of these nutrients are essential for life. Farmers use them to fertilize crops. The problem is that plants don’t absorb all that fertilizer. Instead, excess soaks into the ground or gets washed into rivers when it rains.

Cupped hands filled with eutrophic water by REUTERS/China Daily.

Once these nutrients reach a water body, they cause a rapid, uncontrolled growth. Normally, algae and aquatic plants are limited by how much nitrogen and phosphorus are available. So when they suddenly have an abundance, they bloom like crazy. They form a dense cover across the water surface, blocking sunlight for plants below.

When the algae runs out of nutrients, they die. Bacteria consume the resulting organic matter. In doing so, the bacteria also consume oxygen in the water. This process, called eutrophication, can put a lake in dangerously low levels of oxygen. Fish need dissolved oxygen to breathe. When oxygen levels crash, a healthy ecosystem becomes a dead zone. These dead zones reduce fish populations for generations. This is the leading theory for what killed the fish in Fern Lake.

The Industry Behind the Pollution

For eutrophication to happen, something upstream has to be releasing those nutrients. In the United States, that something is usually agriculture.

The EPA identifies animal manure, excessive fertilizer application, and soil erosion as the main sources of nutrient pollution. The states with the highest nitrate concentrations in their water systems are, predictably, those with the most agricultural activity.

The troubling part I learned is how little of it is actually regulated. The Clean Water Act, the federal law made to protect waterways from pollution, doesn’t regulate nonpoint source pollution. The CWA distinguishes between point source pollution, like a pipe releasing waste directly into a river from a wastewater plant, and nonpoint source pollution, which includes stormwater, urban runoff, and farm drainage. Point sources can be regulated directly, while nonpoint sources like agricultural runoff are managed through ambient water quality standards. Regulators set a limit for how polluted a waterway is allowed to become, and hope everything upstream cooperates. This approach is reactive rather than preventative.

Illustration of nonpoint vs point source pollution, by the EPA Office of Water.

Voluntary programs run by nonprofits, corporations, and state governments try to manage nutrient pollution from farms through incentivizing practices. But, the practices they prompt are optional. Farmers use them only on a small portion of their total cropland.

A Community in Crisis

Agriculture is not only the biggest polluter of freshwater in the US, but also the biggest consumer. The most obvious example is the San Joaquin Valley, one of the most productive agricultural regions on Earth, responsible for about 25% of U.S. food supply. To sustain these farms, groundwater has been pumped so aggressively that the land beneath the valley is physically sinking.

At the same time, the valley’s water supply is severely contaminated with nitrates, which were detected in 97% of wells sampled. Together, groundwater depletion and nitrate pollution have created a drinking water crisis. The communities hit hardest are small, rural, predominantly low-income and mainly Latino.

Tulare County is the center of the crisis. Residents face reproductive health consequences, including higher rates of miscarage, at levels higher than anywhere else in California. On top of health consequences, residents are paying more for water. Households in the San Joaquin Valley spend an average of 4.6% of their income on water, or nearly three times what is considered affordable by the EPA. That money goes to either contaminated tap water, bottled water, or home water filtration systems.

The Price We All Pay

Assigning monetary value to ecosystems is a widely debated topic. But no matter how you feel, nutrient pollution threatens businesses that rely on healthy water. Researchers estimate that freshwater nitrogen and phosphorus pollution costs the United States at least $2.4 billion annually.), with the greatest losses being to property values and recreational uses. The U.S. Geological Survey estimates that removing nitrates from drinking water alone costs the U.S. more than $4.8 billion every year. We’re spending money treating a problem that could’ve been prevented upstream.

Nutrient pollution can also impact aquaculture and commercial fisheries. In the Chesapeake Bay, oysters struggle to survive because of water pollution. A disappearing oyster population could make pollution worse because they are important for filtering huge amounts of nitrogen from the water. Fewer oysters means dirtier water, and dirtier water means fewer oysters. This domino effect threatens the livelihoods of fishermen and the broader economies of coastal communities.

A Better Way to Farm

One of the most effective changes farmers can make is planting cover crops. These are fast growing plants that remain between growing seasons, when bare soil would otherwise have no roots to hold nutrients in place. Cover crops absorb excess fertilizer before it can escape into waterways. Studies show that cover crops can reduce nitrogen leaching by up to 60% and phosphorus losses by up to 95%.

Farming area with bare soil and riparian buffer near Chesapeake Bay by Ben Longstaff, University of Maryland Center for Environmental Science.

Riparian buffers, which are planted areas between a field and a waterway, provide a similar function. They intercept runoff, trap sediment, and absorb nutrients before they enter the waterway.

We don’t have to choose between cleaner water and feeding people. It’s assumed that more fertilizer means a higher crop yield, and reducing input would mean growing less food. But research suggests that the tradeoff isn’t true. Many farms are over-applying fertilizer, and that excess isn’t feeding anyone. It’s just polluting water.

Restoring What We’ve Lost

The best way we could conserve our watershed is by restoring natural systems that once filtered them. Wetlands are a compelling example of this. Often called “nature’s kidneys,” they work by filtering pollutants out of the water. Wetland plants and microbes absorb nutrients directly from the water. Yet the United States (excluding Alaska and Hawaii) has lost more than half of its wetlands since European colonization. And with them, a large capacity for natural water filtration.

Investing in wetland restoration is not only environmentally conscious, but economically smart too. Wetlands are usually less expensive to build and maintain than traditional wastewater treatment infrastructure. A study of wetlands in the Mississippi River Basin found that restoring wetlands in small drainage areas of a watershed could greatly decrease water treatment costs. Once the initial construction investment is paid off, the wetlands could potentially generate $200 million annually.

Arcata wetland wastewater treatment facility by Jill Oviatt, Western City.

A local model sits here in Arcata, where Cal Poly Humboldt resides. The Arcata Marsh and Wildlife Sanctuary treats the city’s sewage through a constructed wetland system, while serving as a wildlife refuge. It also hosts community activities like birding, biking, and hiking (plus water quality fieldwork for classes like mine). Before it was the Marsh, that area of the waterfront was a disused landfill called “Mount Trashmore,” built on top of a former lumber mill and pastures. Its transformation into a cost effective, low energy wastewater treatment center and beloved community space demonstrates that ecological restoration and urban utility can work together.

A Call to Action

What most likely killed those fish is not an isolated event. The same process is happening across the country, in watersheds most people will never see, and tap water people can’t safely drink.

Water pollution is a problem I intend to address as a future environmental engineer, designing green infrastructure and monitoring watersheds. But meaningful change also requires policy to hold the farming industry accountable.

“When the last tree is cut, the last fish is caught, and the last river is polluted; when to breathe the air is sickening, you will realize, too late, that wealth is not in bank accounts and that you can’t eat money.”

– Alanis Obomsawin

I think about the families in Tulare County who can’t drink their tap water. The oyster fishermen whose livelihoods are lost to a contaminated Bay. Every community living downstream from a field that received more fertilizer than the soil could hold. Clean water isn’t a guarantee. It’s the result of choices about how we farm, what we regulate, and who we decide matters.