On my server, when ever I try and go underwater, the screen turns white (like white wool) and the console is spammed with
Client> 2013-07-11 19:52:15 [CLIENT] [SEVERE] ########## GL ERROR ##########
Client> 2013-07-11 19:52:15 [CLIENT] [SEVERE] @ Post render
Client> 2013-07-11 19:52:15 [CLIENT] [SEVERE] 1281: Invalid value