In conclusion, dissolved oxygen is vital to keep aquatic ecosystems healthy. To test this we used a sample from a stream and measured the level of dissolved oxygen to determine if the stream was healthy or not. The results showed our stream sample had 17.8mg/L of DO so all organisms living in that ecosystem will thrive. In the case that the dissolved oxygen number was lower many of the upper tier organisms would have not been able to survive. Our sources of error were human error with measuring the amount of drops to go in the solution which could have affected the mg/L number we got in the end. All in all, the results concluded that a healthy level of dissolved oxygen is important for a stream to keep its organisms alive. If we were to continue with this study in the future we might test multiple streams, healthy vs. unhealthy. We also could question what is the highest and lowest level of DO that organisms can survive in.