There was once a steel-decked river barge, decommissioned and idle in Morgan City, Louisiana. Lonely and unused, it was purchased by the Neptune Foundation, a not-for-profit that constructs movable waterfront pools for recreationally underserved communities. The foundation commissioned Jonathan Kirschenfeld Associates to have at it; and one Hurricane Katrina and about two years of work later, the Floating Pool was sent north to New York. This summer, it's been moored at Hunt's Point, Brooklyn. Next month it will depart New York. Destination: the U.S. Pavilion at the Venice Biennale.