The Guinness World Record for the most canoes and kayaks on water at one time was held by Cleveland Metroparks for seven years. On May 19, 2001, 776 canoes and kayaks was the most canoes and kayaks ever to form a free-floating raft, held together only by hands. Since then, the record has been broken, once by Inlet, New York with 1,104 boats and recently by Pittsburgh, Pennsylvania with 1,800 boats.

A timeline:
1996: 649 boats, Byron, Illinois
2001: 776 boats, Cleveland, Ohio - Cleveland Metroparks
2008: 1,104 boats, Inlet, New York
2010: 1,619 boats, Pittsburgh, Pennsylvania

Help Cleveland reclaim its title from Pittsburgh!

"We’ve come together before, and now it's our time to do it again. Help bring world recognition to Cleveland Metroparks. I'll see you there!" 
- Robert Hinkle, PhD, Chief of Outdoor Education
Thanks to Ralph & Gail for the following:
The 1998 Edition of the Guinness book has the following, along with a picture:

Largest Canoe Raft
A raft of 582 kayaks and canoes, organized by Cleveland Metroparks, was held together by hands only for 30 seconds while free floating on Hinckley Lake, Cleveland, OH on May 21, 1995.