Bridge Builder is the fourth level of Sink or Swim.
First, use the two water pipes to get the two ducks and collectible. (The collectible is located under the algae, in the dirt.) Next, use the pipe on the right to spread the algae to itself. Then, use a few drops of ooze to harden the algae into rock. This will leave the top water pipe open. You can now get the last duck and fill up Swampy's tub.