Float plane pilot reported a near miss with another aircraft at A11 that was on its takeoff run.

Narrative

I was returning from a flight seeing trip with friends. Approaching Campbell Lake; while over Potters Marsh; I transmitted on 122.9 my intentions to conduct a West approach and landing. As I got closer; I saw that the wind conditions favored a southeast landing; so I transmitted my changed intentions to land to the southeast. I also noted [another aircraft] moving on the surface on the east end of the lake. I called him stating; ' Aircraft on the east end of Campbell Lake; [I am] entering a right downwind for a southeast landing.' On downwind I saw another aircraft on short final; also doing a southeast landing. I called him saying that I was turning final over McDonalds; and he responded saying that he was going to the north side but would stay clear while I was landing. Once on the water and with a view around the point of land formed by Arleen Drive; I cleared east and saw [the other aircraft]; nose high; on his takeoff run. I judged that my speed would leave me on a collision course with him; so I went to full throttle; was able to cross his path ahead of him and avoid conflict.