Is the water warm? I remember when my blk/wht Nika was only 4 months old in 1994 and I took her out to an area that had a channel of water running around it and as soon as I got her there she bolted off enthusiastically and didn't see the channel and SPLASH! The look on her face was "What the heck"!! She paddled right outta there, shook off and ran around like nothing had happened.
The water was o.k. I checked it under the knees, but I didn?t swim. Mody saw bigger dogs swimming and playing and I am sure she didn?t know what continues after going deepre to water:) But she was very brave and after few minutes of untrust she went back to water, but only under her belly:)