Crews from RNLI Rye Harbour launched to search for a dog lost in the river on Friday (December 14).
The call from the Coastguard arrived just after 11.20am for the lifeboat to launch.
The distressed owner of the dog had rung 999 for help.
The lifeboat was launched at 11.40am and headed down to the mouth of the river, which was where the dog was last seen.
The boat did two sweeps of the river entrance and later found the dog, which had sadly succumbed to the elements and was found dead at the scene.
The crew recovered it and brought it back to the lifeboat station to which Dave King, the warden of the nature reserve, brought the owners of the dog.
The RNLI advises owners it is best to keep dogs on a lead if they are close to cliff edges or fast flowing rivers.
If the dog goes into the water or get stuck in mud, don’t go after it.
Move to a place where the dog can get to safely and call to it. In many cases dogs will get out of difficulty themselves.
Tony Edwards, lifeboat operations manager at Rye Harbour, said: “We were pleased that the owner of the dog did the right thing and rang for help, which we responded to by sending out the lifeboat.
“The outcome of the rescue was a sad one and our thoughts are with the owners.”