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Little Susitna Water Quality

Summary

The Little Susitna River is proposed for listing as impaired (polluted) for turbidity and petroleum hydrocarbon (gasoline) pollution in an 8.5 river mile stretch upstream and downstream of the Little Susitna River Public Use Facility (PUF) boat launch. Both pollutants are due to motorized boat activity on the river during sport fisheries. The state Board of Fisheries has implemented restrictions on the Little Susitna River not allowing fishing from a boat using a carbureted 2-stroke motor. This action is expected to improve water quality from gasoline pollution. Turbidity pollution is not as easy to fix and an ongoing public and agency dialogue is expected to find solutions. The water quality monitoring reports and other information are linked in the Of Interest box to the right.

Turbidity

Turbidity is a measure of water clarity in streams, rivers, lakes, and the ocean. Turbidity describes the amount of light scattered or blocked by suspended particles in the water sample. Clear water has low turbidity, and cloudy or murky water has a higher turbidity level. Turbidity is caused by particles of soil, organic matter, metals, or similar matter suspended in the water column.

While some turbidity occurs naturally, excess turbidity can have numerous adverse effects on aquatic life and other water uses by decreasing the light penetration for plants, decreasing the visibility of prey and predators for fish, and hiding navigation hazards for boats.

From 2007–2011, DEC conducted turbidity water quality sampling in the lower Little Susitna River during the king salmon (May – June) and silver salmon (July – August) fisheries. Water monitoring found that 7.5 river miles downstream of the Little Susitna River PUF boat launch to approximately 1 river mile upstream of the PUF boat launch is polluted with excess turbidity. Timing of the turbidity impairment is during the peak activity of the salmon fisheries and associated high motorized boat use — late May/June (king salmon fishery), late July/August (silver salmon fishery).

Gasoline

Compounds in gasoline are highly toxic and tend to accumulate in the fats and oils of organisms. This can impact or kill aquatic organisms such as insects that serve as a food source for fish and wildlife. The negative effects of gasoline can move up the food chain from the aquatic insects to fish to wildlife and potentially to humans. Polluted water can also affect fish and wildlife through direct contact and consumption of polluted river water. Because gasoline contains known cancer causing compounds (carcinogens) such as Benzene and Benzo(a)pyrene, controlling their concentration in the Little Susitna River is important not only to protecting the environment but ultimately human health.

From 2007–2012 and again in 2014, DEC sampled water in the lower Little Susitna River during the king salmon (May – June) and silver salmon fisheries (July – September). Water monitoring found that 7.5 river miles downstream of the Little Susitna River PUF boat launch to approximately 1 river mile upstream of the PUF boat launch is polluted with excess gasoline. Timing of the gasoline impairment is during the peak activity of the silver salmon fishery and associated high motorized boat use in August.

The Alaska Board of Fisheries implemented a new regulation effective January 2017 that prohibits fishing from a motorized boat unless the motor is a 4-stroke or direct fuel injected 2-stroke. This action, along with DEC’s Clean Boating public outreach campaign, is expected to reduce the petroleum hydrocarbon levels in the river. DEC is describing the water quality of the Little Susitna River as “threatened” due to petroleum hydrocarbon pollution and will commit to resampling the river once the new regulation is fully implemented and enforced. Once the water quality sampling demonstrates the Little Susitna River is meeting allowed limits, DEC will remove the impairment designation for petroleum hydrocarbons in a future Integrated Report.

Contact

Laura Eldred
Phone: 907-376-1855
Email: laura.eldred@alaska.gov

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