Frøylandsvatnet is a lake located in the district of Jæren in Norway. It forms part of the division line between the municipalities of Klepp and Time. The origin of the name is from the Norse god Frey. The lake is quite shallow, with an average depth of 5.5 m.
The lake is located in an area with very intensive agriculture. Early in the 1980s the lake was identified as being one of the worst cases of eutrophication in Norway. Algal bloom was a widespread problem, and there were cases reported of poisonous algea causing cattle to die from drinking the water.
The release of substances containing nitrogen and phosphorus has since been reduced, but large collections of sediment in the shallow lake causes the problems to decline rather slowly.