The pilot reported that from his airborne perspective, the river looked suitable for landing his float plane. He did not observe any sand bar or obstacles in the water. The pilot stated that his descent into the water was normal, and he landed with the current. Upon touchdown the airplane, which was only equipped with floats, immediately nosed over and sank. The pilot said the front of the right float was ripped off in the landing. The pilot inflated his emergency flotation device and swam to shore.