How is stream health measured?

The health of a stream can be measured in three different ways:

1) Biological: the types and quantities of fish and aquatic insects

2)  Chemical: the types and quantities of chemicals in the water such as pH, conductivity, water temperature, and dissolved oxygen

3) Physical: changes in the shape of the stream (erosion, deposition, head-cutting, vegetation loss etc.)

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What stream health parameters are of greatest concern and importance in Harford County?


1) Sediment: Sediment enters streams from bank erosion and runoff, especially from impervious surfaces. Excess sediment can disrupt fish reproduction and decrease visibility in the water, making it more difficult for aquatic plants to grow. Sediment can also transport nutrients.

2) Nutrients: Excess nutrients, specifically phosphorous and nitrogen, enter streams through stormwater runoff from a variety of sources, such as fertilizers bound to sediment particles. These nutrients leach into the water and cause rapid growth of algae. The dissolved oxygen in the water, which fish need to survive, is reduced as the algae decay. 

Additional resources