Editor’s note: This is the second of a three-part series that explores the history, ecology and future of Stansbury Lake.
Stansbury Lake is a living ecosystem, from the water insects and crawfish living in the bottom to the pelicans fishing near its surface.
While the lake exhibits a diversity of life, including thousands of fish planted two years ago, the system can be fragile, according to Stansbury Park Service Agency Manager Randall Flynn. He has worked with the lake for more than 20 years and has seen the impact of human meddling firsthand.
“Any time you mess with an ecological system, there’s a domino effect,” Flynn said.
While some residents have become frustrated with unsightly weeds and algae blooms on the lake, Flynn said his focus is on striking a balance between aesthetics and the health of the lake.
The biggest challenges for Stansbury Lake are nutrient pollution and dissolved solids, which is the salt content in a body of water, according to Jake Vander Laan, lake assessment coordinator for the Utah Division of Water Quality.
Flynn said Stansbury Lake struggles with high phosphorus loading from external sources as more people have moved in around the lake.
“When this was first built and there were very few people here, there wasn’t a lot of nutrient loading from external sources taking place in this lake,” he said.
Human and animal waste, fertilizer, detergents and pesticides can all add phosphorus to the lake, according to Flynn. For example, if a resident uses granulized fertilizer on their yard and it rains, the fertilizer can be washed away into the community’s stormwater system and eventually the lake.
Nutrient pollution occurs when excessive amounts of nitrogen and phosphorus are present in a body of water, according to the Utah Division of Environmental Quality. While both nutrients contribute to the growth of aquatic plants and algae, too much nitrogen and phosphorus can cause eutrophication, which can impair water quality, endanger aquatic life and reduce oxygen in the water.
But prior to the most significant development along the shores of Stansbury Lake, there was another issue beside widespread algae and weed growth, Flynn said. Lake weeds were a problem in the south side of the causeway, where the lake water was clear, but much of the lake was a milky green color and opaque due to suspended solids.
The service agency determined the source of the poor water clarity was bottom-feeding carp in the golf course ponds, Flynn said. The carp turned over the clay soils in the ponds, suspending solids in the water that flows into Stansbury Lake.
Since water in the golf course ponds could be isolated from the lake, the service agency decided to kill the carp using rotenone. Rotenone is a natural substance used as an insecticide and for fish eradication, according to the Utah Division of Wildlife Resources.
“It had the effect we wanted — it killed the carp in the (ponds) and we did see an increase in water clarity in the big lake,” Flynn said.
Around the same time, the service agency acquired an old lake mower from Fish Lake, which had been used to cut weeds around the boat docks and marinas. After the mower was fixed, it was used by residents to cut the aquatic plants, which are predominantly sego pondweed.
Sego pondweed is a food source for ducks, geese and other aquatic birds, which is found throughout the United States, according to the U.S. Department of Agriculture.
Flynn said the weeds, when cut by the mower, can release loose material like seed pods into the lake that can’t all be claimed by the boat.
The combination of improved water clarity and cut weed debris generated more weed growth and in more far-flung corners of the lake, Flynn said.
“We began to see weed growth in parts of the lake where there had never been weeds before,” he said.
As weeds continued to spread throughout the lake, which interfered with recreation and were not aesthetically pleasing, the service agency looked for a new solution. The service agency eventually settled on triploid grass carp, which eat water vegetation like sego pondweed, Flynn said.
The triploid grass carp don’t reproduce, can eat three times their weight in lake weed, and live about 20 years, according to Flynn. The service agency introduced 3,000 carp into Stansbury Lake over the course of two years.
At first, there wasn’t much reduction in weeds, which continued to spread to new corners of the lake, Flynn said. Eventually, however, the triploid grass carp began to do their job.
“We began … over the next four or five years, to see a decrease in the number of weeds around the lake,” Flynn said.
By the time the fish were introduced in the early 2000s, the service agency had a new lake mower that was more efficient and a full-time employee to man the boat. All the weeds on the lake were below the surface and not impacting water recreation, Flynn said.
What the service agency didn’t anticipate, however, was the carp would completely eradicate all the vegetation from the lake.
“The summer before the fish kill, there were no weeds in the lake,” Flynn said. “You couldn’t find a weed to save your life.”
With no weeds or other aquatic plants, the lake had lower oxygen content in its deeper reaches, Flynn said.
In the winter of 2012, Stansbury Lake froze over completely and remained that way for nearly five months, according to Flynn. Usually the lake will freeze and thaw several times during winter months, he said.
Below the ice, the fish were trapped between poorly oxygenated water and ammonia created by decomposing organic material on the bottom of the lake, Flynn said. The livable space continued to shrink, leading to the massive fish kill, which was revealed when the ice melted in spring 2013.
With all the carp in the lake dead, the weeds began to come back in and efforts to keep pace by mowing the weeds recommenced, Flynn said.
The service agency decided not to reintroduce the carp to see if it would restrict the spread of the weeds in the lake, according to Flynn. The carp ate the weeds but would defecate out seed pods all throughout the lake, further exacerbating the spread of weeds throughout the lake, he said.
In April 2015, a total of 15,000 fish were introduced into Stansbury Lake, including catfish, bluegill, large-mouth bass and crappie.
While the weeds have begun to choke out large swathes of the lake, Flynn said the service agency is looking to balance a healthy ecosystem with the recreational and aesthetic desires of residents.
“We have to be careful when we go after aesthetics because in the past we’ve caused problems trying to make it look better and we’ve actually caused the problem to grow,” he said.
The main culprit behind the excessive weed growth is the phosphorus introduced into the lake by external sources, like fertilizers, Flynn said. He said weed and algae growth in the lake will continue to be high if there is plenty nutrient pollution.
The U.S. Environmental Protection Agency recommends homeowners take steps like cleaning up after their pets, use phosphate-free detergent, use water efficiently and not apply fertilizer on windy or rainy days to reduce nutrient pollution.
“We just have to rely on people, educate them the best we can, and hope that they will cooperate in their practices,” Flynn said.