Shackleford Banks is a small island off the coast of North Carolina where a large group of horses has lived for over 300 years. They survive by drinking from ponds, natural seeps, and holes they dig to reach freshwater underground. But the island is changing, and storms, floods, and dry weather are making it harder to find freshwater. One reason is because salt from the ocean gets mixed in with freshwater which can harm plants and animals and change the land. To learn more, we studied six places where the horses drink. We measured how salty the water was and used cameras to watch the horses. We found that the horses like to drink from the holes they dig because they usually have freshwater. But sometimes the holes run out during dry weather, and the horses must drink from saltier places. Our research helps people better protect wildlife that depend on freshwater on changing coastlines.