I have DD's so its a bit different than running a typical retriever. We expect dogs you use their search, drive, nose and independence in recovering game. In training we release a wing clip duck and unseen to dog throw it into a pond and then bring the dog up. Depending on the water body size, its not uncommon to have dogs recover the birds hundereds of yards away.
But in a more typical retreiver manner, I have worked with my male on lines, 300yd plus on land and to cross a body of water to the other shore (200-250yds) I put that training to test last year and we downed a couple of geese, one landed about 100yd the other sailed about 300+ yards. I sent him on the close bird that he marked and afterwords I sent him on the sailed bird. He got to the first birds scent and I gave him one back command and he stayed on the line and kept swimming, this being on the chesapeake there wasn't any opposte shoreline, I started to regret my descison to send him and began getting ready to pull the anchor when I noticed him get on the scent trail of the wounded goose. The goose had now swam out to about 400 yards, he got to within 50 yards and sighted the goose and went loud (barking) so I new the chase was on and in short order he grabbed the goose and began to come back. The other guys in the boat didn't even know what a DD was when we left the ramp and told me in 40 plus years of hunting that was one of the best retrieves they had seen. I was happy and to cement that retrieve in my head, when the dog came onto shore and sat in front of me, we noticed a shiny metal band on its leg. As we didn't know who hit that bird, being in my boat and the dogs retrieve the band was given to me, my only band.