Average Monthly Merrimack River Water Temperatures 2003 - 2008
The table below gives the average Merrimack River water temperature during the indicated months for the years 2003 - 2008. Management at the PSNH Bow Power Plant kindly calculated these averages and provided them for ARC use. The temperature readings were taken from the north white and blue buoy located at the mouth of the brook just south of and on the opposite side of the river from the white sand beach. This is the metal buoy in the downriver traffic lane that you might have bumped with your boat or smacked with your oar.
Average Monthly Merrimack River Water Temperature Upriver of the PSNH Bow Power Station.
| April | 46.1 |
| May | 56.2 |
| June | 68.4 |
| July | 75.6 |
| Aug | 75.3 |
| Sept | 68.6 |
| Oct | 55.6 |
| Nov | 44.2 |
These temperatures are representative of the river water temperature upriver of the cooling water return inlet. This inlet is located on the west bank just downriver of the power plant. Water temperatures downriver of the inlet will usually be warmer by some unknown amount.
From the table, one could estimate the following, on average, as a rule of thumb. As the temperature goes up in the spring, it crosses 50 degrees on May 1st and 60 degrees on June 1st. As the temperature goes down in the fall, it crosses 60 degrees in early October and 50 degrees on November 1st.
The literature indicates that the risk of cold water shock increases at water temperatures below 60 degrees. This risk increases dramatically at temperatures below 50 degrees. In the absence of actual measurements, river users should take note of these average temperatures and factor them into their decision making.