Afterwards, he became a professor of botany in Berlin, and from 1901 until 1938 was also in charge of the Biological Prussian Experimental and Testing Institute for water supply and sewage disposal.
Kolkwitz is known for work with Maximilian Marsson (1845–1909) in the development of the "saprobic system" as a biological determination of water quality and levels of organic waste (pollution) in rivers and streams.
Their methodology was a non-chemical analysis that was based on patterns of abundance and distribution of various biological species.
The term "polysaprobic" was used for river environments with a large amount of decaying organic matter; "oligosaprobic" described locations with the least amount of organic waste, while alpha- and beta-"mesosaprobic" defined moderately polluted habitats.
Later, this index was expanded into nine zones, with "xenosaprobic" being the least polluted and poly-saprobic" having the highest level of waste.