The Broederstroom, the small montane stream that flows down the escarpment valleys of South Africa’s Limpopo province, eventually joining the Letaba River, is in the dwang. Silt from large-scale farming operations is threatening the water quality and the local trout population. Our Troubled Waters feature from The Mission Issue 45 (May/Jun 24). Photos. Rob Tooley, Kade Thompson, Bronwyn Egan

The waters

The Broederstroom is home to self-sustaining populations of brown and rainbow trout. It’s one of Limpopo’s fly fishing gems, managed by the Haenertsburg Trout Association. It rises in the Woodbush Forest Reserve in Magoebaskloof, at which point it is clean and cushioned by an excellent riparian zone of mature indigenous forest.

Photos by Kade Thompson

After weaving under old lichen-covered trees and through small patches of native grassland, the Broederstroom’s margins become lined by plantations, and more recently established avocado, kiwi and blueberry crops. It’s in these areas that the vegetation composition of the river has been drastically altered.

The worry

Season after season, the Broederstroom suffers severe siltation – when sand or soil blocks its natural flow – mainly caused by agricultural run-off in the river’s catchment, but also by the lack of functional riverbank vegetation. “An intact natural riparian zone ensures the good health of a river’s system by filtering pollutants, preventing runoff and siltation, and mitigating flood damage,” says Dr Bronwyn Egan, a biologist at the Larry Leach Herbarium at Limpopo University. “Legislation exists to ensure that some land converted from forestry should be restored to natural vegetation. This conversion would mitigate some of the possible deleterious effects of commercial orchards as well as silviculture practices in the catchment.”

The silt problem. Photos by Rob Tooley

As part of his research for a master’s degree, Dr Hlulani Hlungwani, who now works as an environmental officer at the Department of Forestry, Fisheries and the Environment found that Broederstroom trout are confined to higher-altitude sites because downstream habitats are uninhabitable as a result of land-use activities that disturb top soil. This causes the accumulation of silt and results in poor-quality static water in the lower reaches.

“Whether the causes are land use, conservation mismanagement, or a lack of scientific research, without pressure from civil society the Broederstroom’s degradation will probably continue.”

Pete Schulenberg, a concerned land owner and fly angler, has witnessed these negative effects on his local fishery. He says, “Over all the years that we have lived on the mountain, our river has been gin clear. Since 2015 or so, large farming companies started cultivating avos. Since then, there has been serious run-off and pollution flowing into the river causing a silt-up. I’m in the lower parts of the catchment, below Dap Naudé Dam, and I get all the silt.”

Photos by Kade Thompson

Pete has seen a gradual decline in trout numbers over the years on his stretch of river. Trout have a sensitive gill and oxygenation system. This is easily clogged up by suspended sediment, a prominent cause of mortality. The lack of clean gravel beds in the lower Broederstroom could also be interrupting successful spawning events. Pete says, “I always stock my river at the beginning of winter. The fish last up until the first rains and then the numbers dwindle. Upstream, the river has less silt and the fishing is immaculate. It used to take about a week to clear, but this brown water can last nearly a full season now.”

It’s not just the trout. Dr Hlungwani’s findings also suggest that populations of elusive mountain catfish (Amphilius spp.) are at risk.

The way forward

Unfortunately, no formal scientific studies have yet exposed the effects of these environmental changes on the quality of the water, and amount of water available, in the Broederstroom. Dr Egan has some ideas about how to shift the conservation. “The existing riparian zone should be conserved where it is in a natural state, and in areas which are overgrown by alien plants, natural vegetation should be restored to create a buffer zone. If the riparian corridors are restored to create adequate buffer zones (20 to 50m wide) and the land use within the catchment above the Broederstroom is sustainably managed, then the water quality will be maintained, promoting the successful ecological functioning of the system.”

Catchment and good grassland around Dap Naudé Dam. Photos by Bronwyn Egan

Whether the causes are land use, conservation mismanagement, or a lack of scientific research, without pressure from civil society the Broederstroom’s degradation will probably continue. Mountain Environmental Watch is one such civil group working to protect water quality and quantity in the Upper Letaba catchment. If you would like to get involved email them at mew@haenertsburg.co.za.

While river legislation does require the maintenance of a good riparian buffer, the specifics of it are vague and unpoliced. Perhaps it’s up to private land owners to pull finger and prioritise riverine health?

This Troubled Waters feature ran in the The Mission Issue 45 (May/Jun 24). Read the whole thing below, for free.