https://phys.org/news/2018-05-edna-method-uk-aquatic-diversity.html

Traditionally, in order to survey waterways, scientists would need to catch the animals themselves. With this new technique, DNA amplification and sequencing can be used to identify which animals have been present in an area of water, all in one test.

The method, could assess the impact of hydropower plants and other barriers on the passage of migratory fish, including threatened species like eels. The arrival and spread of invasive species, which can threaten native species can also be monitored.