Kenai Watershed Forum study links turbidity with boat traffic, levels exceed state standards

File photo by M. Scott MoonKing salmon anglers work the Kenai River in July 2009. A river turbidity study has shown xxxxxxxxxxxxxxxxxx

Editor’s note: This is the first of a two-part series examining a Kenai Watershed Forum study showing violations of state water quality standards on the Kenai River. Sunday’s story will examine community response and a potential impairment designation for the river.



Boat traffic is stirring up enough sediment on the Kenai River to cause violations of state standards for drinking water, recreational use and the health of fish and wildlife, according to a study.

The three-year study, conducted by the Kenai Watershed Forum on contract with the Alaska Department of Environmental Conservation, has yet to be formally released to the public and will not be included in the state’s 2012 biennial listing of impaired water bodies.

The DEC project manager, Tim Stevens, said there is no formal timeline for the release of the watershed forum’s study as he has yet to finish reviewing the data and it must go through several other agency members before being approved.

The problem

Turbidity is a measurement of the amount of light that is scattered as it passes through the water column. The more solids suspended in the water, the less light can penetrate and the cloudier the water becomes.

In photographs taken for the DEC, turbidity manifests as two muddied thick brown stripes along the banks of the Kenai River, which contrast with the normally glacial blue water.

In 2007 while doing a flyover on the river as part of its strategy to combat hydrocarbon problems, Stevens said Kenai Watershed Forum researchers noticed something wasn’t quite right.

“We could see the river with the plumes on the side,” he said. “... That didn’t really look natural.”

The watershed forum has data from 2007 when it began measuring for turbidity after a conversation director Robert Ruffner said he had with the Army Corps of Engineers.

While early results suggested violations of state water quality standards, there had not yet been a baseline of turbidity established on the river to compare measurements against, Ruffner said.

DEC’s criteria for determining water quality impairments requires a measurement of the natural turbidity condition on a river before it will list it as impaired.

When measuring for turbidity, researchers measure the amount of light defracted in the water column rather than the amount of solids suspended in the river.

The state standards for turbidity are measured in NTUs, or nephelometric turbidity units, and Stevens said it’s hard to pinpoint exactly how much mass in a water body is required to raise the NTUs turbidity level.

“It’s a different parameter,” Stevens said. “You can’t do a mass balance and say you need two more pounds of soil in this water to come up with 5 NTUs. You can’t do that. What makes the light scatter — turbidity — includes everything from bacteria, algae, sediment, dissolved organic compounds. Sticks floating on the water, they all affect turbidity measurements. So it’s not just one thing.”

The study

The DEC protects the Kenai River for turbidity in three categories: drinking, recreation, and fish and wildlife.

While Stevens said it was unlikely that anyone was drinking or swimming in the river, those designated uses are easier to violate than turbidity standards for fish and wildlife.

The turbidity levels considered safe for all three uses were exceeded for several hours in July throughout all three years of the study.

The EPA and the watershed forum cite a 2001 study that linked elevated turbidity levels with certain harmful effects on fish such as decreased feeding, reduced size. Higher turbidity can also increase water temperature and reduce the amount of photosynthesis in the water, according to the EPA.

Bruce King, a retired Alaska Department of Fish and Game biologist and member of the Kenai River Special Management Area advisory board, said discussions about harm to the Kenai River tend to be “fish-focused” rather than looking at the entirety of the food chain.

“One thing that probably hasn’t been talked about too much in this situation ... is that the primary fish food species — invertebrate species — on the Kenai River are predominately filter feeders,” King said. “As an aquatic biologist you might wonder how high turbidity impacts their food web.”

When turbidity levels are high and light is diffused, aquatic plants that depend on photosynthesis to survive might suffer as well, he said.

According to DEC, many of Alaska’s waters have naturally occurring turbidity.

Researchers at the watershed forum used data gathered on Mondays, when Alaska Department of Fish and Game regulations restrict motorized boat traffic, and at places in the river where boat traffic isn’t heavy, to establish a natural condition.

Other rivers in the state like Caribou Creek in the Denali National Park are in violation of state turbidity standards based on previous mining in the area; the Nakwasina River in Sitka is impaired due to timber harvesting in the area according to DEC data.

Stevens said a water body cannot be in listed as in violation of state standards for turbidity due to naturally occurring conditions.

“We would only consider listing the river if we found that there was human input that was causing turbidity to be above the natural condition,” Stevens said.

Clearing the water

The watershed forum has continued to monitor turbidity levels on the river, though its contract with the DEC ended in 2010.

During the course of its study for the DEC, the watershed forum documented more than 700 boats in the lower part of the river in one day.

Since then, the watershed forum has begun monitoring a portion of the river continuously to count boat wakes and try to establish a correlation between the number of boats and the number of hours the turbidity standards are exceeded, Ruffner said.

“It kind of gets at the carrying capacity,” Ruffner said. “This is how many boats you can have on the river without it having an impact.”

Researchers have also started gathering data closer to shore, as the study for the DEC gathered data 10-20 feet from the shoreline.

“We haven’t finished doing the statistics on that yet ... but it’s clearly more turbid closer to the shore,” Ruffner said.

The DEC could use the results of the watershed forum study to classify the river in one or more “impaired” categories.

Ruffner and Stevens were involved with the river’s former hydrocarbon impairment designation and said compelling river users to change their behavior was difficult without an official impairment designation.

“A lot of the time you have some resistance. People will say well, if its not impaired it’s not a problem. They’re less willing to work on a solution,” Stevens said.

Ruffner and Stevens agreed that designating the river as impaired gave regulatory agencies more power to change boating regulations on the river, and motivated users to change their behavior.

“No one wants the river to be impaired, Ruffner said. “Everyone wants to see it not be impaired, I mean it’s a world class resource, it should beat all water quality standards out there. I think the general public at-large will recognize that if the state says the water body is impaired, somebody should be doing something.”


Rashah McChesney can be reached at

Exceeding standards

The state's drinking water standard is 5 NTU above natural conditions, the secondary recreation standard is 10 NTU above and the Fish and Wildlife standard is 25 NTU above.

During July, the river exceeded drinking water standards for more than 40 hours during all three years of the study. During the same period of time standards for recreation were exceeded for more than 25 hours and more than eight hours for fish and wildlife according to study data from River Mile 11.5, or Eagle Rock.


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