According to the pilot, the "flight departed VFR from KVQQ at 15:55 for flight to KCRG. After departing Class D airspace to [the] southeast the pilot descended over the St. Johns River approximately 1/2 na[utical] mile offshore to practice reading wind direction from [the] water surface. The winds were very light and [the] water surface [was] mostly glassy. [The] pilot descended from about 2,500 ft. to approximately 100 ft. above [the] water and made several circles to [the] right to view [the] water. [The] pilot then leveled [the] wings and the [air]plane then bounced unexpectedly on the water and made about two more bounces before spinning to the left. [The] aircraft came to a stop and [the] pilot and passenger exited [the] cockpit onto [the] wing and were picked up by a passing motor boat. The plane sank after about 3 minutes." The pilot further stated that "this accident was caused by a glassy water condition and the pilot loosing depth perception. [The] pilot had no intention of landing and was practicing reading water for wind direction where wind was very light or none at all. [The] pilot had been endorsed on September 11, 2007 for SES [Single Engine Sea] practical testing but had not taken [the] check ride."