Although BOD is used in several different ways, we used it as a vehicle to understand and potentially measure some bacteria and other microorganisms that are present in the water but unable to be seen by the human eye. The idea behind the test is that if a water sample is taken and left to sit for 24 hours with the container thoroughly covered and air-tight, any microorganisms in the water will start to use the existing oxygen to live. Covering the container with a material that lets a little light through eliminates photosynthesis, therefore stops any surplus oxygen from being created from algae or other vegetation. After letting the sample sit for 24 hours, the amount of oxygen in the water is tested again. In theory, the greater the difference between the original oxygen amount and the amount left after letting it sit, the higher some microorganisms and vegetation are present. BOD is essential to the health of a river because of what it tells us about the landscape of the river. Without actually examining a water sample under a microscope, it is impossible to say whether a higher BOD is beneficial or detrimental. A higher BOD can be positive for the spinymussel in the way that there are potentially more microorganisms for the mussel to feed on, such as plankton. However, a higher BOD can also be negative if it is bacteria that is using up the oxygen. An abundance of bacteria can be detrimental to a river because it uses up the available oxygen, substantially restricting and suffocating the rest of the organisms in the river including the James River Spinymussel.