Data from: Organic matter loading by hippopotami causes subsidy overload resulting in downstream hypoxia and fish kills

Organic matter and nutrient loading into aquatic ecosystems affects
ecosystem structure and function and can result in eutrophication and
hypoxia. Hypoxia is usually attributed to anthropogenic pollution and is
rarely documented in unpolluted systems, particularly in rivers. Here we
show that organic matter loading from hippopotami causes the repeated
occurrence of hypoxia in the Mara River, East Africa. We documented 49
high flow events over three years that caused dissolved oxygen decreases,
including 13 events resulting in hypoxia, and 9 fish kills over five
years. Evidence from experiments and modeling demonstrates a strong
mechanistic link between the flushing of hippo pools and decreased
dissolved oxygen. This phenomenon may have been more widespread throughout
Africa before hippo populations were severely reduced. Frequent hypoxia
may be a natural part of tropical river ecosystem function, which directly
challenges our notions of the reference state of rivers in the absence of
human influence.