Okay, the game is really interesting with easy game mechanics. And oil spill is a huge issue especially in my country Bangladesh in the Sundarbans oil spill caused a huge issue several years ago. I appreciate you making a game on this.
I would say a different shape for different types of bullets/projectiles would help differentiate it better. And some sort of slow motion effect when successfully cleaning the oil spill. Sound and feedback for able to hit the ducks and oils. A better balanced timing structure would make the game better.
Otherwise good game man.