My Husband And I Were On A Houseboat For A

My husband and I were on a houseboat for a week in Tennessee. My husband now has a pin dot rash over his feet and lower legs-mostly on the anterior aspect. It looks like a petechiae, but the rash blanches and is more dense around his ankles and itches there as well. He was in the lake most days and used sunscreen. He was not sunburned, but did ride in a boat with his "white" legs exposed to the sun for about 30-40 minutes with no sunscreen the day we came home. Any ideas?