In 1972, Congress passed the Clean Water Act (CWA) in response to the unhealthy state of the nation’s lakes, streams, rivers, and coastal areas. At the time, only one third of the nation’s waters were safe for swimming and fishing, eliciting a great amount of public concern. The Clean Water Act is a complex law, but it helps support and fund water quality monitoring, limits pollutant discharge, supports restoration, and protects wetlands. 

One aspect of the CWA is that it helps establish the amount of pollutant a waterbody can receive daily and maintain water quality standards. The process is briefly described below :

1.  Water Quality Assessment. Streams are tested for various parameters, such as bacteria, dissolved oxygen, nutrients, sediments, etc. to see if the water meets state-approved water quality standards. Monitoring can be costly and time consuming, so many streams and rivers have yet to be tested and identified as streams of concern. 

2.  Compile List of Water Quality Limited Streams. Streams not meeting the water quality standards are added to the “water quality limited” list, which is commonly referred to as the “303(d) list” after the section of the CWA that mandates the list. When establishing the 303(d) list, the state agency must consider “all available data.” The majority of streams on the 303(d) list are for temperature, since it is one of the easiest parameters to accurately measure.

3.  Establish Total Maximum Daily Load (TMDL). Once a stream or river has been identified as “water quality limited,” the CWA states that a TMDL must be established for all streams listed on the 303(d) list. A TMDL is the total amount of pollutant from all sources that can enter a waterbody without violating the water quality standard. 

The goal for establishing TMDL’s is to have streams and rivers meet water quality standards. The lack of established TMDL’s and the small percentage of waterbodies on the 303(d) list does not reflect on the cleanliness of our waterways, rather it can be explained by the initiative, money and effort required to go through the process. 

Something important to consider when looking at the 303(d) list of water quality limited waterbodies is how populated the watershed is. Populated areas usually have more roads to access streams, and more concerned citizens living near waterways. One reason for the high number of 303(d) listed streams in Tualatin River Basin (in Washington County, OR) is because of the high population and a high level of monitoring. The Tualatin might not have the same number of water quality limited streams if it were not the most studied watershed in the state. 

Some Factors that can Influence Water Quality:
Point Source Pollution 
Point source pollution is defined as contaminants that are discharged or emitted from an identifiable source. Point source pollution includes output from factory pipes, landfill leachate systems, canneries, domestic sewage, slaughterhouses, tanneries, and factory smokestack to name a few.

Non-Point Source Pollution
Non-point source pollution is contaminants which don't have a single identifiable source.  Parking lots often accumulate trash, sediments, oil and other chemicals from cars, and other pollutants that get directly deposited into waterways during rain events.  This is just one kind of non-point source pollution commonly found in developed areas.

Since the Clean Water Act of 1972 established regulations for point sources that emit or discharge pollution into the waterways, point source pollution has been greatly reduced.  Non-point source pollution is now the primary concern for our waterways. A common culprit of non-point source pollution in residential areas are the fertilizers and chemicals people apply to their lawns in order to keep them green. These chemicals leak into waterways with rain. The combined nutrient and chemical runoff from many homes can have a large effect on stream health.

Loss of Riparian Vegetation
Loss of native riparian vegetation has contributed to degraded water quality and habitat concerns for aquatic life. Without plant and tree roots stabilizing river banks, accelerated erosion occurs, decreasing water quality with increased turbidity levels, increased Total Suspended Solids, and depending upon the geologic setting and land use, greater nutrient levels increasing algae growth. In addition to plants reducing erosion by anchoring river banks with roots, mature trees shade the waterway from the hot summer sun - maintaining cool water temperatures for aquatic life, especially cold water fish like salmonids. Furthermore, mature riparian trees provide woody debris for pool habitat in creeks as branches and logs eventually fall into waterways. Soils associated with riparian vegetation function as a sponge, allowing rainwater to slowly percolate into the groundwater. Groundwater responsible for 60% of base stream flow in the Northwest, and an even greater percentage in times of drought. Healthy soils with riparian vegetation also function as filters, reducing the concentration of pollutants such as bacteria, sediment, fertilizers, and hydrocarbons entering creeks and rivers.