Your Rates, Your Voice
The Mossel Bay Municipal Biodiversity Assessment (2019) provided one of the first comprehensive looks at the area’s aquatic ecosystems. It identified key rivers — including Twee Kuilen, Hartenbos, Klein Brak, and Groot Brak — as vital ecological corridors feeding the bay’s estuarine and marine systems. Yet, the assessment also revealed a worrying trend: many riparian zones are degraded, wetlands have been filled or altered for agriculture, and stormwater systems have replaced natural drainage.
By 2024, a Specialist Freshwater Assessment (Hilland & Confluent Environmental) reinforced those concerns. Even small wetland depressions were found to be “heavily modified,” often losing natural hydrological function due to landform alteration. Several systems fall within Freshwater Ecosystem Priority Areas (FEPAs) — meaning they are essential for maintaining aquatic biodiversity — yet they remain vulnerable to continued disturbance.
Collectively, these findings show that Mossel Bay’s rivers are not just local features; they are part of a regional hydrological web whose health underpins marine productivity, groundwater recharge, and community resilience.
Alien invasive plants such as Acacia mearnsii (black wattle), Populus (poplar), and Eucalyptus species have colonised much of Mossel Bay’s riparian zones. According to Le Maitre et al. (2016), invasive alien plants reduce South Africa’s total surface runoff by roughly 1,444 million cubic metres per year — nearly 3% of national water availability.
These invaders are particularly damaging in the Garden Route, where dense stands of wattle and gum trees line streams, outcompeting native vegetation. Their higher evapotranspiration rates drastically reduce streamflow, starving downstream wetlands and estuaries. Furthermore, as Chamier et al. (2012) explain, many invasive plants alter nutrient cycles by fixing nitrogen and releasing organic acids that change soil chemistry. The result: a chain reaction that lowers dissolved oxygen levels and alters microbial communities vital for water purification.
In Mossel Bay’s smaller catchments, these effects are magnified. Reduced surface flow means less dilution of pollutants, while thick invasive growth destabilises banks, increasing erosion and sedimentation. This combination leads to declining fish and invertebrate diversity — a key sign of ecosystem collapse.
Mossel Bay’s rapid population growth and tourism-driven economy have increased water demand dramatically. Municipal reports estimate that between 2005 and 2024, household and industrial extraction more than doubled. Much of this demand is met through surface and groundwater abstraction from the Hartenbos and Groot Brak catchments.
The Department of Water and Sanitation has repeatedly warned that over-abstraction lowers base flows — the consistent trickle that sustains river life during dry periods. When base flows drop, water temperatures rise, oxygen levels fall, and pollution concentrations spike. Native species such as the Cape kurper (Sandelia capensis) and the smallscale redfin (Pseudobarbus asper) are particularly sensitive to these changes.
Meanwhile, urban expansion has sealed off natural infiltration zones. Impervious surfaces, such as roads and pavements, accelerate runoff, leading to flash flooding during storms but prolonged drought conditions in between. The ecological rhythm of Mossel Bay’s rivers has been disrupted — alternating between drought and deluge.
Pollution is the invisible thread running through every driver of biodiversity loss. Municipal wastewater, agricultural runoff, and stormwater drains all converge into river systems that eventually discharge into the bay.
In several catchments, nutrient enrichment has caused eutrophication — excessive algal growth that depletes oxygen. According to the Garden Route Biosphere (2023) State of Knowledge Report, periodic algal blooms have been observed in the Klein Brak and Hartenbos estuaries, especially after heavy rains flush urban pollutants into the system.
Microplastics and heavy metals are also emerging concerns. Sampling near the Hartenbos outfall has revealed microplastic fibres in both water and sediment, suggesting that Mossel Bay’s pollution footprint is not just chemical but physical. These particles can accumulate in aquatic organisms, moving up the food chain and eventually entering the marine ecosystem.
Freshwater systems in Mossel Bay feed directly into estuaries and the coastal marine zone — meaning inland degradation quickly translates to oceanic decline. Increased sedimentation and nutrient runoff cloud the bay’s nearshore waters, reducing sunlight penetration and harming seagrass meadows that serve as nurseries for juvenile fish.
Research by Le Maitre (2016) and Chamier (2012) confirms that loss of vegetated riparian buffers worsens this problem. Without these “green filters,” pollutants move unimpeded into estuaries, altering salinity and causing fish kills during low-oxygen events. In extreme cases, estuaries can flip from net exporters of organic material (healthy systems) to nutrient traps (degraded systems).
As local fish stocks decline, fishermen notice smaller catches, and seabirds that rely on river mouths for feeding also disappear. The consequences ripple outward — ecological degradation becomes economic loss.
Climate change compounds existing pressures. Rainfall patterns in the Southern Cape have become increasingly erratic, with long dry spells punctuated by intense downpours. This variability stresses river ecosystems that depend on steady seasonal flows.
Prolonged droughts lower water tables and dry out wetlands, while flash floods erode banks and wash pollutants into the sea. Warmer water temperatures further exacerbate algal blooms and invasive plant growth. The combination of climate stress and human pressure is pushing freshwater ecosystems beyond their recovery thresholds.
If adaptive measures — such as riparian restoration, alien-clearing, and water-saving infrastructure — are not implemented soon, Mossel Bay could see permanent loss of its freshwater biodiversity within a generation.
Each of the referenced studies contributes a layer of scientific credibility:
Mossel Bay Biodiversity Assessment (2019): Establishes baseline conditions, identifies key threats, and recommends management zones.
Hilland & Confluent Environmental (2024): Confirms degradation and loss of ecological function in specific wetland and river systems.
Le Maitre et al. (2016): Quantifies national water-flow reduction due to alien plants, illustrating the link between invasion and hydrological stress.
Chamier et al. (2012): Explains how invasives alter water chemistry, compounding pollution impacts.
Garden Route Biosphere (2023): Provides current observations on river health and pollution trends in the broader region.
Together, they form an evidence-based picture: Mossel Bay’s freshwater ecosystems are declining primarily due to cumulative human pressures, not a single catastrophic event. Recovery is possible, but only through coordinated, science-based management.
To reverse biodiversity loss, three urgent interventions stand out:
Riparian Rehabilitation and Alien Clearing:
Expand Working for Water-style programmes in the Hartenbos and Groot Brak catchments. Clearing invasive species restores flow, stabilises banks, and revives native vegetation.
Pollution Control and Stormwater Reform:
Upgrade wastewater infrastructure and enforce buffer zones between agriculture and waterways. Introduce green infrastructure — reed beds, bioswales — to naturally filter runoff.
Community-Led Monitoring and Data Transparency:
Establish an open-access online dashboard for water quality and biodiversity indicators. Local residents, schools, and NGOs can contribute citizen-science data, enhancing accountability and awareness.
These steps require both political will and public participation. If implemented, they could turn Mossel Bay into a model of coastal-catchment rehabilitation for the Western Cape.
Environmental recovery depends on culture as much as policy. Schools, community organisations, and local businesses have a pivotal role to play. Integrating environmental education into curricula, hosting “adopt-a-river” campaigns, and supporting local clean-ups foster ownership and long-term engagement.
Collaboration between the Mossel Bay Municipality, Garden Route Biosphere Reserve, and CapeNature is vital. By aligning restoration targets with national biodiversity goals, these institutions can pool resources, reduce duplication, and ensure that restoration projects deliver measurable ecological benefits.
Mossel Bay’s freshwater ecosystems are approaching a tipping point. The evidence from local and national studies paints a clear picture: alien species, over-extraction, and pollution are converging to undermine both ecological and social well-being. Yet, this crisis also presents an opportunity — to rebuild rivers as living systems that support biodiversity, livelihoods, and recreation.
Through coordinated action, transparent governance, and community-based stewardship, Mossel Bay can restore the lifeblood of its environment. Every drop of clean water that reaches the bay’s estuaries is a testament to local resilience — and to the belief that environmental decline is not inevitable, but reversible.