Portland — Water Temperature, Sea Conditions & Trends

Water Temperature: Daily Trends, Historical Records, and Forecast

⚠️ As of today, the minimum water temperature ranges from 60°F (15°C) to 65°F (18°C). The water is comfortable for most people, making it an ideal range for water sports enthusiasts. The temperature does not cause significant discomfort, and swimming will be pleasant for the majority. However, it's important to remember that prolonged exposure to the water can still lead to cooling, so it's essential to monitor the time spent in the water, especially for children or elderly people.

It is important to note that these swimming tips and recommendations apply only in good weather. When the air temperature is below 68°F (20°C), and sometimes even below 77°F (25°C), swimming can be unpleasant even with relatively high water temperatures.

Water Temperature Chart Over the Last 30 Days

Water temperature in Portland rose over the last 30 days but fell over the last week. Currently, the sea water temperature at this location matches the average for this day in previous years.

According to our forecast, Water temperature in Portland will be 16.8°C in the next 7 days. See the table below for daily data for the upcoming week.

Table of Daily Sea Temperature Data

Annual Water Temperature Overview by Month

Monthly Water Temp Ranges

30°C

25°C

20°C

15°C

10°c

5°C

0°C

Annual Water Temperature Trend

Portland, Maine sits on the inner edge of Casco Bay and experiences a marked seasonal swing in coastal water temperatures. Winter surface waters commonly hover near freezing, roughly 0–4°C, while spring brings a gradual rise into the single digits, often about 3–10°C by late spring. Summer is the warmest period for swimming, with typical sea surface temperatures in June through August ranging from around 10–18°C and occasional sheltered pockets reaching nearer 20°C during heat anomalies. In autumn the water cools again, usually falling to roughly 8–12°C as the air chills and storms stir the bay. Tidal flows, wind-driven currents and the deeper Gulf of Maine influence these values, so short-term variability and cool upwellings are common even in summer.