Michigan Compiled Laws, Chapter 259. Aviation § 259.8

(a) “Seaplane” means an aircraft that is capable of landing and taking off on the water.

(b) “Seaplane base” means an area of water used or intended to be used for the landing and takeoff of aircraft, together with appurtenant shoreside buildings and facilities.

(c) “State approach surface” means an imaginary plane longitudinally centered on the extended runway centerline and extending outward and upward from each end of the state primary surface.

(d) “State primary surface” means a surface longitudinally centered on a runway. For a paved runway, the state primary surface extends 200 feet beyond each end of that runway for an unpaved runway or a planned paved runway, the state primary surface ends at each end of that runway. The elevation of any point on the state primary surface is the same as the elevation of the nearest point on the runway centerline. The width of a state primary surface is as follows: