Identifying factors that harm fish and other aquatic life is a key part of the watershed restoration and protection projects. The department identifies factors that harm fish in lakes.

Many waters suffer from stressors that harm fish and other aquatic life. These stressors may also affect recreation, such as swimming and fishing.

What conditions stress our water?

Too much sediment

Soil and other matter in water can make it hard for fish and other aquatic life to breathe, feed and reproduce. Sediment can also cover spawning areas and fill in parts of streams. Excess sediments can cause damage by blocking light that allows algae to grow, harming fish gills, filling up important habitats and stopping fish from seeing well enough to move around or feed.

Low oxygen

Aquatic life needs oxygen dissolved in the water to breathe and survive. Oxygen molecules dissolved in water are a major indicator of water quality. Like the air we breathe, the survival of aquatic life depends on a sufficient level of oxygen dissolved in water. When it drops below levels necessary for sustaining aquatic life, it becomes a significant water quality impairment, often referred to as low dissolved oxygen

Temperature

Stream temperature affects metabolism and the ability to get oxygen, especially for species such as trout. Water temperature exerts a major influence on biological activity and growth, has an effect on water chemistry, can influence water quantity measurements and governs the kinds of organisms that live in water bodies.

Lack of habitat

Habitat affects all aspects of survival for fish and other aquatic life. Habitat encompasses places to live, food to eat, places to reproduce and means of protection. Habitat loss, due to destruction (filling in wetlands or dredging rivers), fragmentation (dams or water diversions), or degradation of habitat (pollution or invasive species), is the primary threat to the survival of wildlife in the United States. 

Chloride

Chlorides from road salts and other sources can stress or even kill aquatic life. Chloride occurs naturally in lakes and streams, and many organisms need it to carry out the basic functions of life. But elevated levels can cause cells to lose water and become deprived of nutrients, ultimately killing fish, amphibians, plants and other aquatic organisms.

Too many nutrients

Excess nutrients, such as phosphorus and nitrates, can be toxic to aquatic life and cause algal blooms that can smell bad, block sunlight and in some cases, release toxins. Algae feed on the nutrients, growing, spreading and turning the water green. 

Bacteria and Pathogens

Excessive amounts of bacteria or pathogens are typically a symptom of anthropogenic influence on a stream. This is usually accompanied by one or more of the stressors mentioned above.

Heavy Metals

Heavy metals from mining operations or other sources can be toxic to aquatic life. Types of heavy metals commonly found in water include manganese, lead, arsenic, chromium and copper. Some of these are essential for healthy biochemical function, however metals such as lead, chromium and arsenic can be toxic when ingested in small or large quantities.

Unknown

Some things that stress aquatic life may not be known or currently measured. Pesticides, herbicides, pharmaceuticals and altered hydrology are all things that can be difficult to quantify in streams to know to what extent they are affecting aquatic life. Additionally, new emerging contaminants can also cause stress to aquatic systems.