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Mashomack Musings: Freezing waters

As the thermometer falls, cold temperatures race to solidify our watery habitats. Here at Mashomack Preserve, the frozen landscapes take many forms, from solidified freshwater kettle ponds to skim ice offshore in the Peconic. But not all of these water bodies freeze in unison. Why?

To answer this, we have to think like chemists. The main compound that slows the freezing pace of water in our local bodies of water is salt. When salt is added to pure water, it slows the freezing process and lowers the temperature at which it will become a solid.

Most folks think of water freezing at 32 degrees Fahrenheit or 0 degrees Celsius, and that’s true for freshwater. 32 degrees is also the melting point for ice, meaning that water is in a constant state of flux.

However, there are three types of water around the Island: fresh, salt and brackish (a mix of fresh and salt). Freshwater is the gold medal winner when it comes to freezing. Saltwater freezes about 4 degrees lower, at 28.4 degrees, earning the bronze medal. The unique areas of brackish water along the coastlines where salt and fresh water battle it out to earn a silver medal, freeze somewhere between 28 and 32 degrees, depending on the amount of salt present.

But as our climate shifts and our winters warm, frozen waters are becoming fewer and farther between because we need multiple days at or below the freezing point for the solidification of the water to outpace the melting of ice.

Join us for a winter walk along the Red Trail, where you can spot all three of our medal holders — fresh kettle ponds, brackish marsh and the salted waters of the Peconic.

Want a fun experiment to do at home? See below for some easy-to-follow instructions: 


• 3 cups (make sure they are freezer-friendly and close in size) 

• Salt 

• Spoon (any size will do)

• Tape 

• Pen / washable marker

• Clock


1: Label your cups using a piece of tape or a washable marker so you have a “Fresh Water,” “Brackish Water,” and “Salt Water.”

2: Fill each cup up halfway with tap water. 

3: Add 1 spoonful of salt to your “Brackish Water” cup. Mix well until you dissolve as much of the salt as you can.

4: Add 3 spoonfuls of salt to your “Salt Water” cup. Mix well until you dissolve as much of the salt as you can. 

5: Place your three cups in the freezer for 4 hours (or overnight if you prefer). 

6: Check your cups to and record your results. See if you can answer the questions below: 

Did all three of the cups freeze?

If not, which cup(s) froze?

Make a prediction: How much longer will it take until your other cups are frozen?

Once you have finished your at-home experiment, don’t forget to make some observations outside. Take your findings to the field and come on a winter hike at the Preserve to see if you can identify the different bodies of water.

Mashomack Preserve is owned and operated by The Nature Conservancy, a global environmental nonprofit working to create a world where people and nature thrive. Our mission is to conserve the lands and waters on which all life depends. To learn more, visit nature.org.