Neponset Brook Trout Study: Final Report

During the course of this study, we surveyed trout at over 60 sites, assessed 113 culverts, and engaged 54 volunteers in over 1000 volunteer hours!

Embrace-a-Stream volunteer, Will Friedland

In September 2021, we completed our three-year Embrace-a-Stream study of cold-water fish, which investigated the distribution of brook and brown trout in the watershed and habitat quality.

Working in partnership with Greater Boston Chapter of Trout Unlimited (GBTU), we surveyed trout at over 60 sites, assessed 113 culverts for fish passage, monitored water temperature, dissolved oxygen, and habitat characteristics, and engaged 54 volunteers in over 1000 volunteer hours!

Thank you to everyone who participated!

Read Embrace-a-Stream Final Report

The goals of the Embrace-A-Stream project were to:

  • Develop a restoration plan that would support the native eastern brook trout
  • Provide volunteer opportunities for GBTU and NepRWA members to familiarize themselves with the streams in the Watershed
  • Map the distribution of trout within the watershed
  • Monitor stream temperature, dissolved oxygen, and other habitat characteristics that are important to the different life-history phases of trout.
  • Locate and evaluate passage barriers including dams and culverts
  • Identify riparian lands that could be restored or protected

In the summer of 2020 and the spring of 2021, we sampled eDNA at multiple sites along 14 streams within the Neponset River Watershed and the samples were analyzed at the University of Maine.

eDNA stands for environmental DNA. It is the DNA that sloughs off organisms and in the aquatic environment. It can be collected in water samples and analyzed to determine the different species that occur in the vicinity of the water sample.

Brook trout rely on certain habitat features to survive and complete their life history phases.  For example, they require cool water temperatures and coarse substrate.  Stream temperature was monitored at 45 sites to identify locations that have temperatures that harm or even kill trout.

Additionally, in the spring and summer of 2021, we collected monthly habitat data on stream characteristics that we identified as being important for trout survival, such as maximum pool depth and substrate type.

Habitat data was collected monthly at 21 stream sites within eight waterbodies from April through August of 2021: Beaver Brook, Ponkapoag Brook, Mill Mine Brook, Purgatory Brook, Germany Brook, Mill Brook, Traphole Brook, and Pine Tree Brook.  We selected 10 sites that had positive brook trout eDNA results from 2020 and 11 sites that had negative eDNA results so that we could compare differences in habitat.

Stream barriers like dams and culverts prevent fish and other aquatic organisms from moving within the watershed.  Removing the obstruction can open up important habitat for foraging or spawning that was previously inaccessible.

We documented the location of culverts at the nine streams in our study: Beaver Brook, Germany Brook, Mill Brook, Ponkapoag Brook, Pine Tree Brook, Purgatory Brook, Traphole Brook, Tubwreck Brook, and Mill Mine Brook.

Culverts were scored for their environmental impact.  Long narrow culverts with large drops are more impactful than wide culverts with natural stream bottom and the scores reflected this. In addition to the culvert documentation and scoring, we compiled data on dam location from the Office of Dam Safety and from a watershed-wide dam survey that NepRWA completed in 2000.

Project successes:

Despite the challenges of organizing volunteers during the pandemic, we engaged 54 volunteers over 38 data collection days for a total of 1,156 volunteer hours (see the table below for a breakdown of the volunteer activities).

We surveyed trout at over 60 sites in the Spring of 2020 and then again in the Summer of 2021, assessed 113 culverts for fish passage, and monitored water temperature, dissolved oxygen, and habitat characteristics.

Activity Volunteers Trained Volunteer Hours
2019 Culvert Assessments 20 375
2020 eDNA 13 66.5
2020 Temperature Logging 21 315
2021 eDNA 13 75.5
2021 Habitat Assessments and Temperature Logging 26 324
Total 54 1,156

Some big findings!

  • Brook trout occur in five streams:  Beaver Brook, Ponkapoag Brook, Traphole Brook, Germany Brook, and Pine Tree Brook. NO brown trout were found!
  • Brook trout streams had cooler temperatures in the spring and summer. The highest average 7-day maximum in streams with trout in the summer was 24.23°C and in streams without trout in the summer was 27.84°C, a difference of over 3°C.
  • Warm water temperatures became too high in the summertime in most streams and restoration efforts could include reducing water, streamside tree planting initiatives, and reservoir release adjustments.
  • We also found that undersized culverts and dams pose a major problem in our watershed.  See the table below for how many culverts occur on each stream and how severely they restrict the movement of aquatic organisms. Connectivity efforts could focus on replacing undersized culverts, removing certain dams that connect trout populations, and assessing stream diversions to ensure they do not impact trout movements.

The table below shows the number of culverts assessed in each stream.  The label on each column refers to the level of impact that the culvert has on aquatic possibility (i.e., Significant = a significant barrier to passage). Bolded rows are the streams with brook trout eDNA.

Additionally, we identified a total of 1,784 acres of riparian area as potential sites for land conservation (see table below). An additional 209 acres of land were identified as potential sites for riparian restoration projects. These calculations consider any land within 100ft of a stream, defined as the riparian corridor.

The amount of land identified for conservation and restoration by waterbody. The total acres of riparian buffer within each subwatershed followed by the number of parcels displayed in parentheses. We divide restoration into two categories of undeveloped open space and impervious areas because of the implications of restoration difficulty.

Waterbody Conservation acres (parcels) Restoration: undeveloped open space acres (parcels) Restoration: impervious acres (parcels)
Beaver Brook 256 (24) 0.6 (2) 1 (2)
Germany Brook 82 (16) 8.1 (21) 4.2 (12)
Mill Brook 60 (27) 0 0.2 (1)
Mill Mine Brook 297 (113) 4.2 (8) 1.2 (4)
Pine Tree Brook 389 (26) 5.5 (12) 11.8 (10)
Ponkapoag Brook 333 (20) 7.2 (18) 1 (4)
Purgatory Brook 200 (41) 62.9 (15) 84.5 (22)
Traphole Brook 167 (34) 9 (13) 7.6 (9)
Total 1,784 (308) 97 (89) 112 (66)


Next steps:

  • In this study, we identified stream reaches that support brook trout (no brown trout were identified).  There is a clear impact of temperature, which appears to drive the distribution of trout on the tributaries.
  • We have identified stream barriers that create connectivity problems between extant populations, potential headwater habitat, and Neponset River access, which would allow for migration between tributaries.
  • Finally, we evaluated habitat at sites in the watershed that both support an extant brook trout population and that do not support a population to identify differences between the two groups.

With all this data, we compiled a series of recommendations that can be used to plan future projects and future studies.

Our final report shows the list of recommended next steps that will help further restoration goals in the watershed.

Jenny Rogers, NepRWA River Restoration Director – December 2021

For additional information about the Embrace-a-Stream Project, please contact NepRWA Executive Director, Ian Cooke, at

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