I received the following information from Dr. Andrew Deacon, Project Manager: Small Vertebrates Savanna Unit, KNP.
Crocodile River: A very diverse river – biggest problem: alien invasive weeds. Regulated by the Kwena Dam, over-utilized by irrigation and extraction for towns. Results in low flows during winter and sometimes no flows near Komati Poort. Since the last irrigators and Mozambique require water, Department of Water Affairs strive to get water to the end of the river, which benefits the park. Return flows from irrigation and pollution due to sewage effluent renders river eutrophic, thus the large amount of green algae covering sensitive habitats. No fish species lost yet.Thank you! A definition taken from Wikipedia: A eutrophic body of water, commonly a lake or pond has high primary productivity due to excessive nutrients and is subject to algal blooms resulting in poor water quality. The bottom waters of such bodies are commonly deficient in oxygen, ranging from hypoxic to anoxic.
Sabie River: Short river from Drakensberg to Mozambique; many dams in catchment (tributaries); very diverse, cold finger running through Park. Water relatively clean, never stopped flowing. Corumana Dam will be heightened, might result in similar problem as Massingir cause in Olifants. Fish reasonably secure.
Olifants River: Water quality problems – mining in catchment. Coal in highveld, heavy metals in Steelpoort and Phalaborwa areas. Erosion in catchment (especially Sekhukuneland) results in major sedimentation in river, covering large stretches of original habitat. Over-extraction of water in in catchments, periodical no-flows in river during winter. Raising of Massingir Dam results in crocodile and fish mortality due to stagnant system. At least 2 fish species absent from river due to state of the river.
Letaba River: Main problem is dams in catchment and over extraction due to irrigation. During low flows just a trickle or no flow. Increase problems with water quality as irrigation return flows increase fertilizer levels in water – resulting in eutrophication. Non flows reduce habitat availability. One fish may be lost to the river.
Shingwedzi: Seasonal river – not too impacted from outside.
Luvuvhu River: Erosion and sedimentation, and low flows due to extraction for irrigation seems to be the main cause for concern. Stopped flows during droughts. No fish lost yet.
I hope this straw dog helps – please feel welcome to ask questions on the frame provided.
Dr Andrew Deacon (SANParks)
Project Manager: Small Vertebrates Savanna Unit, KNP