Once the game starts back the speed off to the blue and red line. Don't touch the speed for the rest of the game. Just use the arrow keys to play. You have to barely skim the water. You also have to get down low over the fires to put them out. Usually it takes 3 trys to extinguish the fires but it can be done in 2 trys before advancing to the next round. By the way, if you go into your, "Documents and Setting" folder you can find under one of the users, usually the administrator, the game called, "waterplane.swf" in there and place it on your desktop. The game is almost the entire screen and it makes it easier to play. You also don't have to keep going back to the website for it.
The trick is to fill up completely, stay low under the first flock, fly in the middle of the screen over the second flock, drop low to hit the fire, then climb to the middle of the screen and accellerate to max speed. Skip filling up again as you should have enough to douse it the second time. As soon as you go feet dry over the fire island, decellerate to min speed, drop after the second flock and douse again. 2 water drops should be enough to douse the fire.
Most of the score comes from the time bonus, so speed is essential.