Germishuys, Ryno, and Roger Diamond. “Nitrogen Isotopes of Eichhornia Crassipes (water Hyacinth) Confirm Sewage As Leading Source of Pollution in Hartbeespoort Reservoir, South Africa”. South African Journal of Science, vol. 118, no. 7/8, July 2022, doi:10.17159/sajs.2022/11098.