Environmental DNA, or eDNA, is an emerging technology that enables scientists to map all the organisms in a river or lake with a small water sample. For around US$50-150, you can learn from one sample all the species passing by the river from a kilometre upstream within the last 24-40 hours. Previously, it took highly intrusive and time-consuming methods to understand species distribution. In comparison, eDNA is more sophisticated (requiring just a single cell of genetic material from an organism), cheaper and easier.
The next step in the technology’s development would to more beyond gauging species distribution to estimating species abundance based on the DNA quantities in samples.