The Knysna Estuary

21 Jan 2015

The Knysna Basin contains an extensive body of water, commonly known as the Knysna Lagoon, which has been integral to the development of the coastal town of Knysna. Fed principally by the 64km long Knysna River, originating in the nearby Outeniqua Mountains, the Lagoon covers some 1.827ha from the river mouth (the Knysna Heads) to the rapids at Charlesford.

Knysna estuary

Technically the Lagoon is in fact an estuary – estuaries are permanently linked to the ocean whilst lagoons are only seasonally so (as a result of temporary sand bars). Scientists refer to the Knysna Basin waters as a “marine embankment” with estuarine characteristics! I think for the purposes of this blog I’ll settle for the Knysna Estuary.

In terms of conservation significance the Knysna Estuary is rated as the most worthy of protection in South Africa! Estuarine productivity and biodiversity are extremely high and what remains of the Knysna salt marshes are second in size only to those found at Langebaan! The Knysna River’s catchment area is over 300 sq km in size and, together with its tributaries, the river delivers over 100 cumecs of fresh water into the Estuary annually. This inflow is the principal reason for the high productivity and biodiversity of the estuarine waters – upon which the entire estuarine aquatic food chain hinges.

Knysna estuary view

The Knysna Estuary is a major contributor to the nation’s fishing industry – both in terms of commercial and subsistence estuarine catches and as a nursery to several important marine line fish species such as kob and rapidly diminishing species such as spotted grunter, Cape stumpnose and white steenbras. Additionally the Estuary is a major source of energy-rich material for those marine fish populations just seawards of the Heads. Despite the somewhat overzealous human encroachment on the estuarine environment via extensive property developments, the remaining salt marshes are still some of the largest remaining nationally. These fragile ecosystems are vital in the maintenance of marine ecological balance – a host of marine fish species depend on the salt marches at some point in their life cycles. The vegetation of the salt marshes, principally eel grass, acts both as a buffer to erosion and as a source of energy and nutrients within the estuarine ecosystem.

Dock at Knysna estuary

 The Estuary is home to one of only three populations of the Knysna seahorse (Hippocampus capensis), the only known estuarine species in existence globally. Wetland bird species have been severely impacted by human encroachment – fortunately biodiversity remains high despite the decrease in population numbers. The impact of indiscriminate collection has reduced pansy shell urchin populations dramatically and Sanparks now conduct regular patrols in an attempt to bring this damaging practice under control.

Birds eye view Knysna estuary

The Estuary played a significant role in the expansion of the Southern cape’s timber industry. Despite the difficulties of navigating the treacherous Knysna Heads, a harbour was established in the early 19th century, principally for the purposes of local timber exports. Modern day developments have transformed the estuarine landscape dramatically as Knysna has evolved into a tourist playground. Future uncontrolled environmental impact on this priceless estuarine asset will hopefully become a thing of the past now that the entire area falls under the watchful eye of Sanparks as the Knysna Lakes Area within the Garden Route National Park. We trust that the Bambo Guest House Knysna guests will keep in mind the fragility and significance of the estuarine ecosystem whilst enjoying the extraordinary beauty of the Knysna Basin.