fastcompany:

What’s so difficult about building a floating pool, you ask? What distinguishes +Pool from a big, expensive above-ground pool is its filtration system. +Pool’s team wants to actively improve the water quality of the East River, by constructing the pool out of a unique series of filters that would make the notoriously toxic waters fit for humans. The pool would release 500,000 gallons of filtered water back into the channel every day. And after a year of testing systems in the river, the team feels confident enough to install a test pool, with a tentative goal of opening the +Pool in summer of 2015. Beyonce, they hope, will play opening day.

Similar project: Copenhagen Harbour Bath
http://www.archdaily.com/wp-content/uploads/2009/01/1668480784_bad-casper-dalhoff-01.jpg