text: Contamination of the lake environment by chromium started in the 1950s, and has increased dramatically until at least 2005, reaching 20 times natural background levels.  It originates in industrial activities that involve leather tanning in the shoe factory of Calzado Cobán. The chromium does not seem to accumulate along the food chain, as it is not found in fishes and crayfishes.  However, it accumulates massively in water hyacinth roots and, from there, is transferred to lake sediments through shedding of roots to the lake floor. Most of the water hyacinth biomass is actually extracted from the lake to fight eutrophication and turned into horticultural fertilizer.