PHysical
There are many characteristics of a healthy stream or river. The physical characteristics of a healthy stream has mixture of rocks like cobble, gravels, sand, and silt will support large variety of life. Also stream can support a larger variety of organism if there is a variety of submerged objects like rocks. When judging the health of a river look for erosion on the banks, if the banks are stable your stream is healthy. If there is grass and trees it can help hold the sediment from going into the river and help filterer out pollution.