Watershed Health


The Department of Environmental Protection (DEP) measures the health of our streams using the  Stream Conditions Index .

The Stream Conditions Index measures the aquatic biological community and ranks the stream according to four categories (like a report card). DEP took the results from studies of the biological community and put them on the map below. 


Montgomery County Stream Conditions 2011 - 2015

Examine the health of over 150 subwatersheds in the County using the Interactive Map below by zooming in or searching by address.



Key to the stream conditions map:
Color code for the stream conditions map.


Map Exports


​Stream Conditions are determined by  sampling of stream fish and bugs. Fish and bugs live in streams year round and are subject to any the changes in water quality or habitat that might occur. If conditions are poor, sensitive fish and bugs can’t survive and won’t be found in that stream the following year. 

After sampling fish and bugs, the resulting data, including the number and types or organisms, are input into an Index of Biotic Integrity (IBI).  IBIs are multi-metric (utilizing several measurements) equations that rate a waterbody with a unitless score.  These scores can then be used to determine if the stream is in Poor, Fair, Good, or Excellent condition.

  • Poor stream condition is a combined IBI score (fish and bugs) of 0-41.  Poor conditions most often occur in places where changes made by humans to the natural environment have substantially altered the structure of the biological community.  These areas are often highly developed or urban and don’t have good stormwater management.

  • Fair stream conditions have combined IBI scores of 42-63.  These conditions occur most often in places anthropogenic stressors have impacted an area, but the area still supports viable biological communities.  This  condition describes many streams in suburban areas with some stormwater management, as well as areas that have had major agricultural impacts.  The biological communities in fair streams are dominated by species that are tough and can survive in most conditions, but may have a few organisms that are sensitive to stressors left.

  • Good conditions are described by combined IBI scores of 64-88.  These conditions are often found in the less developed areas of the county, suburban areas with the latest stormwater management techniques, and areas with lots of protected land in their watershed.  Many of the County’s sensitive species can survive in these streams.  Stream bugs like dragonflies and caddisflies are common.  Fish like sculpins, darters, and longnose dace are common in these streams as well.

  • Only Montgomery County’s best streams are rated excellent and must have a combined IBI score of 89-100.  Most often, only highly forested watersheds with minimal development are in excellent condition.  Here our most sensitive fish and stream bugs live.  Fish like trout, shield darters, and comely shiners are found.  Highly sensitive stream bugs like stoneflies and mayflies are common in these watersheds.


Image of a eastern box turtle Streams with a diversity of fish and aquatic bugs are also great habitat for other wildlife


Montgomery County searched for, and recorded information from, the healthiest streams or those “most recovered” from historic land disturbances remaining in the County to establish the stream conditions index. All County streams are measured against this ‘yardstick’ to better understand the overall health of the stream. County watersheds are sampled on a rotating schedule and are visited at least once every 5 years.