Merrimack watershed bacteria results: August 25, 2026
The citizen scientist samplers of summer are here to bring you important information about the
upper Merrimack River watershed.
River quality monitoring results are here for your weekend plans.
Dear river and watershed friends,
With these last sampling results, the bacteria monitoring season closed this week for the Upper Merrimack Monitoring Program sites from Franklin to Bow, comprising the Pemigewasset, Winnipesaukee, Contoocook, and Merrimack Rivers.
We know that you have heard it before but it’s important to remember that the results shown below are the probable number of E. coli colonies for every 100 millilitres (ml) of water at that moment in time. We call it a snapshot because conditions at that moment are represented and anything that happened a day or so before or after this sampling date can change drastically. All warm blooded animals (including we humans) have E. coli in their guts. That means that bacteria are an indicator that poop has found its way to the water. This could be a result of stormwater runoff, failed septic systems, mis-connected pipes that are meant to transport household waste to a treatment plant, pet or wildlife waste from river watershed, and other sources.
To protect public health, State of New Hampshire designated swim beaches are not allowed to exceed 88 colonies of E. coli per 100ml. Class B waters (all of our sites are designated as Class B) shall not exceed 406 colonies. These designations do not always reflect real-time water quality. The designation indicates what uses, e.g., swimming, fishing, should be supported by maintaining water quality.
This week’s analysis synopsis…
These samples were taken after another stretch of dry, sunny weather. All of the sites met New Hampshire’s Class B standard for recreation and drinking water after treatment. All met the standard for designated swimming beaches. Dry weather sampling is often helpful in identifying illicit connections to the river and its watershed, which might otherwise be masked by polluted rain and snowmelt runoff.
This trend monitoring is important but is a snapshot in time. Pollutants can be present in a river system and then clear in a day or in minutes. Leonardo da Vinci said it best, “When you put your hand in a flowing stream, you touch the last that has gone before and the first of what is still to come.”
You hear us say often, “When it rains, it’s poor,” which means that you may wish to wait a day or so after it rains before recreating in a surface water.
Here are the details.
| Site number and description | results |
| #1 Pemigewasset R. at Route 3, Franklin | 16.1 |
| #2 Winnipesaukee R. at Trestle, Franklin | 24.6 |
| #3 Merrimack R. above FWWTF, Franklin | 43.5 |
| #4 Merrimack R. below FWWTF, Franklin | 28.8 |
| #5 Merrimack at Jamie Welch, Boscawen | 83.3 |
| #6 Merrimack at US Route 4, Boscawen | 45.7 |
| #7 Contoocook R. at Rivco, Penacook | 73.3 |
| #8 Merrimack R. at Sewalls Falls, Concord | 40.2 |
| #9 Merrimack R. at Manchester St., Concord | 57.6 |
| #10 Merrimack R. at Blue Seal, Bow | 69.7 |
| #11 Merrimack R. at Garvins Falls, Bow | 58.6 |
Please join us inrecognizing and thanking our Adopt-a-River Site Sponsors that make this work possible.
Aries Engineering
Elektrisola
Essex Hydro
Gideon Asen LLC
Granite Shore Power (two sites)
GZA Environmental
Watts Regulator / Webster Valve
Winnipesaukee River Basin Program (two sites)
We have two mainstem and several smaller sites available so please contact us if you are interested in becoming a site sponsor.
Our gratitude to Winnipesaukee River Basin Program for their continued support, including covering sample processing costs, taking samples, and providing a safe and convenient drop-off area. The Department of Health and Human Services Public Health Laboratory does a wonderful job processing our samples with prompt results.
A big thank you to Chantal McGuire who continues to make a major trek from her homeplace to Franklin and then to Concord to assure that samples are transported quickly and under controlled conditions.
Did you know that the Upper Merrimack Monitoring program is staffed and managed 100% by volunteers? This means that throughout the year, volunteers organize and perform activities including water sampling, collecting benthic macroinvertebrates to gauge long-term river health, and work nights in a laboratory to identify those “bugs.” If you want to learn more or get involved, please contact Michele and Steve (see below for contact information).
This was the last day of E. coli sampling for 2026. We are so grateful to everyone—and we have started planning for 2027 already/
Please visit our forum at MerrimackRiver.org/forum and the Upper Merrimack Watershed Association site MerrimackRiver.org for further information. Don’t hesitate to contact us at UMMP@MerrimackRiver.org or 603.796.2615 (landline) should you have any questions.
Sincerely,
Michele L Tremblay Stephen C Landry
Program Manager Sampling Supervisor