A delicate balance of oxygen levels in Lake Powell affects the fish that live in the water, and scientists are monitoring whether recent changes in the chemical makeup of the lake could affect habitat and water quality.
Bridget R. Deemer, a research ecologist at the U.S. Geological Survey's Grand Canyon Monitoring and Research Center, told St. George News that Lake Powell's water quality can experience significant changes, depending on a variety of factors.
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Deemer explained that the lake is an "oligotrophic ecosystem," which is a marine ecosystem with low nutrient levels.
Deemer's office has reportedly observing larger and more frequent low dissolved oxygen zones developing in the reservoir.
"This is of concern for fish populations and water quality concerns associated with it," Deemer said. "The water is really clear. It's what you would picture as an ideal place to swim. That has to do with the fact that it doesn't get a lot of nutrient input, so there are no high levels of algal production.
"I would also say that we're observing some big changes on Lake Powell," she said. "We're starting to see increased frequency of these low dissolved oxygen events, where, when the water comes up in the spring, sediment from the deltas is mobilized."
Deemer is watching the oxygen levels to see whether they will increase the risk of algae blooms, particularly toxic ones.
"It impacts the reservoir itself because it changes the habitat for fish because fish breathe dissolved oxygen. They need oxygen in the water, so they'll tend to avoid low dissolved oxygen zones like that," Deemer said.
So far, so good at Lake Powell, but she says lower oxygen levels can happen on large bodies of water.
"We know that these occur or have occurred on Lake Mead and need regular monitors for algal toxins," Deemer said. "I'm just trying to better understand these low oxygen zones and what it might mean for the algae."
In 2015, 2022 and 2023, Lake Powell experienced events with a low dissolved oxygen zone. Deemer said these incidents were "big enough and at the right depth that they impacted the tailwater ecosystem below Lake Powell."
Additionally, there was an open file report in 2015 on Lake Powell about Mercury accumulation in fish. Deemer said visitors would want to know about the water quality since they often fish at Lake Powell.
"This affects, obviously, the quality of fish, if you're going fishing, to actually eat the fish," Deemer said.
Deemer also collaborates with the National Park Service and the Bureau of Reclamation to study Lake Powell's water quality.
Mary Plumb, public affairs officer for the Glen Canyon National Recreation Area and Rainbow Bridge National Monument, told St. George News that the primary factor contributing to the low dissolved oxygen levels in Lake Powell is high spring runoff. The runoff water carries a lot of organic matter, and the breakdown of this organic matter consumes oxygen, resulting in low dissolved oxygen levels and impacting the local fish population.
"The low dissolved oxygen zones tend to be deep in the water column. Most fish during summer months occupy the upper portions of the water column," Plumb said.
Plumb added the potential consequences of decreased oxygen levels for the growth and health of algae blooms in Lake Powell occur when nutrients are excessive and water temperatures are warmer during summer months.
In addition to the National Park Service's water monitoring, the Bureau of Reclamation works in concert with the U.S. Geological Survey to conduct tests on the lake.
"When sampling, Reclamation collects data on temperature, specific conductivity (salinity), dissolved oxygen, pH, turbidity (suspended sediment), depth and light extinction," said Alex Walker, civil engineer with Bureau of Reclamation’s Upper Colorado Basin Region. "Additionally, we collect water samples to analyze for nutrients, metals, and ions, along with phytoplankton and chlorophyll samples. The program provides important information on water quality parameters to inform operational and management decisions."
As for the Bureau of Reclamation's testing of oxygen levels, Walker said the impacts on algae growth is inconclusive.
"Reclamation has a program to monitor dissolved oxygen concentrations in Lake Powell as part of its overall water quality work. There is potential for algal blooms in Lake Powell, particularly in side channels and bays where temperatures are higher and water exchanges more slowly with the main body of the reservoir, but the impacts of low dissolved oxygen on possible algal blooms is unknown."
