A pollutant is generally defined as any substance introduced into the environment that adversely affects the usefulness of a resource or the health of humans, animals, or ecosystems. State agencies have identified the pollutants of major concern in the watershed as sediment, nutrients, bacteria, and heavy metals. Pollutants of lesser concern include acids and pesticides.

Sedimentation is the movement of soil particles carried in rain water into the water bodies of the watershed. This is also referred to as soil erosion. Sedimentation is a natural process, usually involving only minor movement of soil. However, in the Grand Lake Watershed, there is a significant amount of sedimentation which is adversely affecting water quality. Increased sedimentation is caused by disturbance of the natural vegetative cover of the soil. Agriculture, construction, mining and urbanization are the primary causes of increased sedimentation in the watershed. Sedimentation is the major transporter of nutrients.

Nutrients are food or chemicals that an organism needs to live and grow or a substance used in an organism’s metabolism which must be taken in from its environment. Nutrients are naturally present in the environment. Nutrients are a concern when there are sufficient quantities to cause excessive algal growth, a condition that currently exists throughout the watershed. Nutrients needed for algal growth are calcium, carbon, hydrogen, magnesium, nitrogen, oxygen, phosphorus, potassium, and sulfur. Phosphorus is the nutrient for which there is the greatest potential for reduction. Major sources of phosphorus in the watershed are fertilizer, livestock, poultry, wastewater treatment plants, domestic animal and wildlife waste, human waste, decomposed plant material, storm water run-off, and phosphates in automatic dishwasher detergents.

Bacteria of concern come from the intestines of warm-blooded animals. Heavy rains wash animal waste into the waterbodies. Animal sources include livestock manure, poultry litter, wildlife, and domestic animals (horses, dogs, and cats). Human sources include waste water treatment plants and failed septic systems.

Heavy Metals found in the water primarily are a result of past mining activities in the watershed. The Spring River Watershed in particular is home to many abandoned mining operations known as the Tri-State Mining District. Also, the Tar Creek mining area in Ottawa County, Oklahoma, is a U.S. Environmental Protection Agency Superfund site.