There were instances of swimmers itch last summer. The itch is caused by a microscopic worm that tries to burrow into your skin. The itch is caused by the bodies reaction to this worm.
The life cycle of the worm includes ducks and geese. Please be considerate of your neighbors and don’t feed them.
Here is a link to more info from a Calvin Collage study
The State has info here.
Life cycle of swimmers itch.