Merrimack watershed bacteria results: June 16, 2026

The citizen scientist samplers of summer are back 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,

Opening day for the season was June 16, 2026. Upper Merrimack Monitoring Program volunteers kicked off the season with 100% of the eleven sites sampled 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.

Some of these results are higher than we are used to seeing. Some volunteers reported seeing turbid or cloudy water, probably from runoff due to the the recent rains. Only Site 5 exceeded the New Hampshire’s Class B standard for recreation and drinking water after treatment.

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	107.6
#2 Winnipesaukee R. at Trestle, Franklin	93.4
#3 Merrimack R. above FWWTF, Franklin	111.2
#4 Merrimack R. below FWWTF, Franklin	155.3
#5 Merrimack at Jamie Welch, Boscawen	435.2
#6 Merrimack at US Route 4, Boscawen	116.9
#7 Contoocook R. at Rivco, Penacook	69.7
#8 Merrimack R. at Sewalls Falls, Concord	116.0
#9 Merrimack R.  at Manchester St., Concord	155.3
#10 Merrimack R. at Blue Seal, Bow	172.3
#11 Merrimack R. at Garvins Falls, Bow	65.0

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).

Volunteers will take their next samples on Tuesday, June 30, 2026.

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, Program Manager
Stephen C. Landry, Sampling Supervisor