The Jacobson Phenomenon is where two bodies of water, of different constituency pass each other resulting in a distinct pattern on the surface of the water. This can ocur where, for example, one element of the water has a higher saline content than the other, or this can be due to natural water flow or water temperature. The phenomenon is most commonly seen in estuaries where fresh water and salt water can mix or come into contact, but can also be seen in other bodies of water where conditions, such as temperature and wind causes different parts of the water to act in different ways.

Originally this phenomenon was discovered by Jacob Jacobson of Norway.