​Dissolved Oxygen (DO) was crucial to measure because the initial DO in the water was used to calculate biochemical oxygen demand (BOD), which was the amount of oxygen available in a body of water for organisms to consume. This is an important variable because it indicates the amount of oxygen that organisms, such as mussels and fish, can consume. DO was tested by collecting 10 random samples and then sticking a Vernier optical DO probe into a capped, free of oxygen flask of each sample. The DO value then appears on a Lab Quest and was written down. The probe was then washed off with distilled water and the process was repeated.  DO readings were usually anywhere between 90% and 100%, according to the Lab Quests.  Unfortunately, most second DO readings (taken in the lab days later) were often above the initial DO readings taken in the field, and so as a result, the BOD readings resulted as negative, which was highly improbable. The DO of a river can be affected by a multitude of factors. These include phosphates, temperature, flow rate, and turbidity. More phosphates in a river can cause algal blooms which initially create oxygen in the river but as algae dies and bacteria breaks down, the dead plant material oxygen is quickly used up and thus the amount of oxygen left in the water is greatly diminished. Temperature also affects the amount of oxygen in the water because warm water holds less oxygen. The molecules in a warmer substance are more active than they are in a cooler substance meaning that the molecules can more easily be expelled from the water thus less oxygen can be held in warm water.  Flow rate affects DO because water that is moving faster mixes with the air which is a scenario where a lot of oxygen could be dissolved into a river. Finally, Turbidity can affect DO indirectly because cloudy water absorbs sunlight more easily and thus is subject to become warmer. Warmer water holds less oxygen.