Merrimack watershed bacteria results: August 22, 2023

Dear river and watershed friends,

Day 6, the final event of our of bi-weekly 2023 water quality monitoring season saw an expected decrease in E. coli colony counts after a relatively dry and sunny period with some rain preceding the Tuesday, August 22, 2023 sampling day. We got through the season with 100% samples collected by 100% of its volunteers at eleven sites from Franklin to Bow.

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 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.

Sample results are close to the background levels of less turbulent times. We find field replicates interesting. One can see, sometimes, a difference in the Site 2 sample and its replicate. It underscores that these samples are snapshots in time, and something can happen right before or right after you take a sample. These data are important for trend analysis and to help us understand correlations between weather and bacteria counts. 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.  This summer, that means most of the time. 

Here are the details.

Site number and descriptionresults
#1 Pemigewasset at Route 3, Franklin122
#2 Winnipesaukee at Trestle, Franklin52
#3 Merrimack R. above FWWTF, Franklin41
#4 Merrimack R. below FWWTF, Franklin86
#5 Merrimack at Jamie Welch, Boscawen97
#6 Merrimack at US Route 4, Canterbury52
#7 Contoocook at Rivco, Penacook52
#8 Merrimack at Sewalls Falls, Concord86
#9 Merrimack at Manchester St., Concord41
#10 Merrimack at Blue Seal, Bow63
#11 Merrimack at Garvins Falls, Bow52

field replicate for Site 2 value is 10

Please join us inrecognizing and thanking our Adopt-a-River Site Sponsors that make this work possible (listed in order of their sponsored sites 1-11).
Watts Regulator / Webster Valve
Franklin Savings Bank
Winnipesaukee River Basin Program (two sites)
Nelson Analytical
Essex Hydro
Aries Engineering
GZA Environmental
Granite Shore Power (two sites)

Our gratitude to Franklin Waste Water Treatment Plant for their continued support, including covering sample processing costs, and providing a safe and convenient drop-off area. The Public Health Laboratory did a wonderful job processing our samples with prompt results. Thank you, Chantal McGuire for your sample courier-ing from Franklin to Concord.

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 is our final sampling day of 2023 but the work continues with collection and analysis of benthic macroinvertebrates from late summer in the field and over the winter in the laboratory.

Please visit our forum at and the Upper Merrimack Watershed Association site for further information. Don’t hesitate to contact us at or 603.796.2615 (landline) should you have any questions.


Michele L Tremblay                          Stephen C Landry
Program Manager                             Sampling Supervisor