Unlike landplane operations at airports, seaplane operations are often conducted on water areas at which other activities are permitted. Therefore, the seaplane pilot is constantly confronted with floating, objects, some of which are almost submerged and difficult to see - swimmers, skiers, and a variety of wa tercraft. Before beginning the takeoff, it is advisable to taxi along the intended takeoff path to check for the presence of any hazardous objects or obstructions. Thorough scrutiny should be given to the area to assure not only that it is clear, but that it will remain clear throughout the takeoff. Operators of motorboats and sailboats often do not realize the hazard resulting from moving their vessels into the takeoff path of a seaplane.To accelerate during takeoff in a landplane, propeller thrust must overcome only the surface friction of the wheels and the increasing aerodynamic drag. During a seaplane take off, however, hydrodynamic or water drag becomes the major part of the forces resisting ac celeration. This resistance reaches its peak at a speed of about 27 knots, and just before the floats or hull are placed into a planning attitude.Several factors greatly increase the water drag or resistance: heavy loading of the air craft, or glassy water conditions in which no air bubbles slide under the floats or hull, as they do during a choppy water condition. In extreme cases, the drag may exceed the available thrust and prevent the seaplane from becoming airborne. This is particularly true when oper ating in areas with high density altitudes (high elevations/high temperatures) where the en gine cannot develop full rated power. For this reason the pilot should also practice takeoffs using only partial power to simulate the long takeoff run usually needed when operating at water areas where the density altitude is high and/or the seaplane is heavily loaded.5.A heavily loaded seaplane takes off under high density altitude requires （ ） takeoff run.