Healthy waterways The level of dissolved oxygen (DO) in a stream or river is an important indicator of the water's ability to support aquatic life. A researcher measures the DO level at 15 randomly chosen locations along a stream. Here are the results in milligrams per liter (m}): 4.53 5.04 3.29 5.23 4.13 5.50 4.83 4.40 5.42 6.38 4.01 4.66 2.87 5.73 5.55 ? A mean dissolved oxygen level below 5m, puts aquatic life at risk. Do we have convincing evidence at the a = 0.10 significance level that aquatic life in this stream is at risk?