Contributed by Washington Department of Fish & Wildlife

Spilled oil can be devastating to fish and wildlife. Floating oils impact animals at the water’s surface while non-floating oils can threaten underwater habitats and species. Unfortunately, there is no way to capture and rehabilitate animals living underwater that get affected by spilled oil.

Cleaning up oil in underwater habitats is difficult. Removal of sunken oil generally requires dredging out some of the sediment material on the bottom of the river, stream, or lake. Oil on logjams or tree roots in the water may be particularly difficult to locate and removing the oil may cause more harm than good.

Freshwater habitats include lakes, rivers, streams, and wetlands. These habitats are home to about 67 fish species in our state, including one species found only in Washington – the Olympic mudminnow.

Numerous mammals, birds, amphibians, reptiles, and insects rely on freshwater habitats to survive and thrive. Developing fish eggs are particularly sensitive to the effects of oil contamination. Sunken oil also has the potential to kill aquatic vegetation, which can greatly disrupt ecosystems that rely on these plants.

Benthic organisms are animals that live on the bottom of a lake or river, and include organisms such as crayfish, freshwater mussels, snails, sculpin, catfish, and insect larvae. These animals can be smothered by pools of sunken oil.

Other animals in the food web that rely on benthic organisms for food can consume toxins when they eat contaminated prey or aquatic vegetation. For example, mammals such as beaver, muskrat, and river otters frequently dive and forage for food below the water’s surface. This behavior places them at risk from non-floating oils that are in the water column or on the bottom. Likewise, birds that dive or spend large amounts of time wading in water such as diving ducks, heron, and dippers are at risk of getting contaminated with non-floating oil.

The beds in Washington’s freshwaters can generally be categorized by their sediment type:

Fine sediments (mud/silt/sand) accumulate in slow or still water, or, pools. Sunken oil will tend to settle, collect, and remain in fine sediment habitats. During times of low water flow such as late summer or during a drought, pools serve as refuge for fish and mobile aquatic invertebrates and these pools may collect sunken oil. Aquatic vegetation such as lily pads, cattails, and submerged vegetation is frequent in fine sediment habitat. This habitat supports both warm-water fish such as bass, Olympic mudminnow, catfish, and cold-water fish such as trout and salmon. Other species that use this habitat include lamprey larvae, dabbling ducks, muskrat, beaver, California floater, frogs, newts, northwestern salamanders, and turtles.

Great blue heron (Ardea herodias) and turtles in a pond with a fine sediment bottom. Photo by Amy Hallman.
Rough-skinned newt (Taricha granulosa) prefer slow or still water such as this pond with a fine sediment bottom. Photo by Jim Cummins.

Coarse sediments (gravel/cobble) are found in moderately moving water with larger grain-sized bed materials. Aquatic vegetation may or may not be present. Gravel beds can provide spawning habitat for anadromous and resident salmonids such as rainbow, cutthroat, bull trout, salmon, and steelhead. The turbulent water may suspend finer sediment material which can mix with non-floating oils and can cause the oil or settle where the water slows such as in backwater eddies, side channels, undercut banks, and logjams. This habitat also supports both warm and cold-water resident fish, beaver, harlequin ducks, western pearlshell mussel, crayfish, and tailed frogs.

Bull trout (Salvelinus confluentus) is a char native to the northwest that prefers habitats with coarse sediment and moderately moving water. Photo by Eric Anderson.
Adult lamprey (Petromyzon sp.) spawn in river gravels. Photo by Kevin Fox.


Bedrock tends to be found in fast water and contains little or no deposition of fine or coarse sediments. Aquatic vegetation is uncommon in this habitat. During high flows non-floating oil is likely to be flushed through this habitat to an area and may leave a film of oil on the bedrock. This habitat supports cold-water fish, American dippers, harlequin ducks, and torrent salamanders.

American dippers (Cinclus mexicanus) dive in fast-moving rocky streams to feed on benthic invertebrates. Photo by Jim Cummins.
Torrent salamanders (Rhyacotriton sp.) can be found in mountain brooks, seeps, and the saturated splash-zone of streams. Photo by Allison Cook.