Interpreting Dissolved Oxygen Data

• low concentrations indicate poor water quality and unhealthy ecosystems
• high concentrations indicate good water quality and healthy ecosystems.

Here is a selection of interpretations for dissolved oxygen results:

• The Global Water Sampling Project in New Jersey states that a dissolved oxygen level of 9-10 mg/L is considered very good; at levels of 4 mg/L or less, some fish and macroinvertebrate populations begin to decline.

• The Hach Chemical Company suggests that a dissolved oxygen content of 4-5 mg/L is considered borderline for aquatic life over extended periods of time. Sportfish populations require 8-14 mg/L and good fishing waters generally average 9 mg/L. At less than 3.0 mg/L, bottom-feeding fish (suckers) will die. While northern pike require at least 6.0 mg/L in the summer, these fish can get by with as little as 3.1 mg/L in the winter.

• The 1999 Canadian Water Quality Guidelines (CWQG) for the Protection of Aquatic Life suggest that total oxygen concentrations for freshwater should be 5.5-9.5 mg/L.

• According to "Stream Analysis and Fish Habitat Design", sportfish have differing requirements for dissolved oxygen at different temperatures:

  Fish Species	Temperature°C	Minimal Dissolved Oxygen mg/L	Optimal Dissolved Oxygen mg/L
  Brown trout	colder than 15 warmer than 15	at least 3 at least 5	more than 7 more than 9
  Pike	warmer than 15	1
  Rainbow trout	15	less than 3 is lethal	7

• "Save Our Streams" states that trout need at least 6 mg/L at all times to function normally. At less than 3 mg/L, the water is considered oxygen poor.

• The FEESA "Aquatic Invertebrate Monitoring Program" states that 4-5 mg/L is the minimum value necessary to support aquatic life.