Water from many bores in central Australia contains nitrate ions. Usually nitrates in rivers, and groundwater are a sign of pollution, or come from agricultural fertilisers. However, in central Australia with a sparse population and little application of fertilisers, this cannot be the case. Researchers have found that blue-green algae (cyanobacteria) in soil produce nitrates. Termite mounds were also found to have staggering concentrations of nitrates, and with heavy rain, the nitrates can be leached down into the water table.