A yellow buoy is a cautionary buoy. I don't believe you can moor on this buoy.
Specifically, a yellow buoy marks a place for boats to anchor.
A bouy is an floating object on water specially placed to inform, aid or warn the oncoming vessels anchored to the bottom. Buoys maybe be cylindrical, conical or in a pillar form. Buoys may also be in form of flags. Some buoys are equipped with light and sound, if the vessel cannot spot the buoy during fog and darkness. Different kinds of buoys convey different messages to the oncoming vessels. Buoys with circles indicate speed limits. Buoys with diamond shapes indicate to keep out of the port as it may be prohibited. Buoys with white lights indicate safe waters. A red and white flag indicates a scuba diving in progress. Yellow buoys indicate danger areas, such as military areas, sea plane bases, race courses. It indicates that the area is not safe to go through.
Its in the water and sinks to the floor of the stream. It means there's too much metals in the creek or stream. The first sign is to test the water and check the iron levels. Second the rocks will turn orange and if it gets really bad everything will turn yellow. Including the rocks the edges of the stream even sticks that been siting in the stream. Theres a formula for this that includes fools gold, iron, and the pH levels.