Answer:
pier
Explanation:
In this text, there are several things that the seaplane could have passed before increasing speed. Usually seaplanes are docked close to the shore along a dock or pier.
After taxiing away from the dock, the floatplanes generally pass the end of the pier and, once in open water, increase speed to prepare for takeoff.
Another possibility could be buoy since these often mark the end of shallow water and the expanse of deeper water more appropriate for takeoff.
