Swimmer's itch is getting under our skin - uncomfortable but harmless 'duck itch' You can't see them when you step out of the water after a swim, but boy can you feel them later. Swimmer's itch (cercarial dermatitis)--also known as "duck itch" or "lake itch"--is microscopic parasites lurking in lake water, capable of causing a... Written By: Brainerd Dispatch | × Swimmer's itch symptoms can be alleviated with over-the-counter antihistamines or anti-itch creams. Special to Forum News Service You can't see them when you step out of the water after a swim, but boy can you feel them later. Swimmer's itch (cercarial dermatitis)-also known as "duck itch" or "lake itch"-is microscopic parasites lurking in lake water, capable of causing a skin rash that's itchy, scratchy and uncomfortable.