River ecosystem threat status

Freshwater (inland aquatic) realm

Nancy Job1 , Andrew Skowno1, 2 , Jock Currie1

1. South African National Biodiversity Institute

2. University of Cape Town

Published

December 5, 2025

Rivers are among the most threatened ecosystems in South Africa, with over 65% of river types categorised as Threatened. This places the vital ecosystem services they provide and the incredible biodiversity they support at great risk.

Sandy banks and riparian forest along the Luvuvhu river within Kruger National Park. (© Nancy Job)
65%
of river length
Threatened
65%
of 222 river ecosystem types
Threatened

Of South Africa’s 222 river ecosystem types, 22% (49) are Critically Endangered, 19% (44) are Endangered, 23% (52) are Vulnerable, and 34% (77) are of Least Concern. In terms of total river length, 2% is Critically Endangered, 6% Endangered, 56% Vulnerable, and 34% is of Least Concern.

Figure 1. Ecosystem threat status for river ecosystem types. The inset graph shows the number of ecosystem types per threat status category.
Table 1. Ecosystem threat status of river ecosystem types.

Ecosystem threat status varies across geomorphological zones with 67% of lowland river types being Critically Endangered compared to only 25% of mountain stream types.

Figure 2. River ecosystem threat status within each geomorphological zone (slope category). (a) The percentage of ecosystem types per category (labelled with the number per type); (b) the percentage of river length (km) within each threat category, providing an indication of the relative extent of each category.
Table 2. Threat status of river ecosystem types summarised by geomorphological zone. Note that extent figures represent river length (km) and have been rounded.
Critically Endangered Endangered Vulnerable Least Concern
Mountain stream Count 6 15 13 22
Extent (km) 640 2 352 1 113 2 716
Upper foothill Count 13 11 15 20
Extent (km) 16 833 7 616 11 855 40 269
Lower foothill Count 11 9 12 26
Extent (km) 10 269 3 199 14 559 47 100
Lowland river Count 19 9 12 9
Extent (km) 10 643 2 348 1 884 6 128

Download the data here.

Important note on work in progress

The river threat status assessment applied the IUCN Red List of Ecosystems framework for the first time. Given the application of a new method and input data, the current results are considered preliminary and a more extensive review of the outputs is still to be completed, with stakeholder engagement continuing through early 2026. It is likely to result in adjustments and an updated assessment, which will be widely communicated.

Approach

Ecosystem threat status is a headline indicator established to assess how close an ecosystem type is to collapsing (losing vital aspects of its structure, function, or composition). It serves as an indicator of the degree to which ecosystems are still intact.

Key input layers include river ecosystem types and river ecological condition.

The assessment was conducted using the IUCN Red List of Ecosystems framework (version 2), which has been applied across all realms for the 2025 assessments. The framework uses the concept of ecosystem collapse as the equivalent endpoint to species extinction. It evaluates the status of each ecosystem type using a set of quantitative and qualitative criteria linked to the key aspects of ecosystem decline, namely, Criterion A: reduction in extent, Criterion B: restricted distribution, Criterion C: environmental degradation and Criterion D: biotic degradation. Read more about this indicator on the ecosystem threat status explainer page.

The IUCN RLE (version 2) approach was followed and the following criteria were assessed for river ecosystems:

  • Criterion B1aiii was applied using extent of occupancy calculations with ongoing decline defined as an increase in the extent of D,E and F condition river length from the previous PES assessment period.

  • Criterion D2b was applied using the rate of change in condition between 2018 and 2024, projected forward to 2068 (a 50 year period).

  • Criterion D3 was applied to the Present Ecological State (PES) data such that Severity >=90% was assigned to PES classes E-F; Severity >=70% was assigned to PES classes D-F; Severity >=50% was assigned to PES classes C-F.

Each river ecosystem type was assessed against these criteria and the highest risk category triggered by any single criterion was assigned as the overall ecosystem threat status for that type. Each of the 222 river ecosystem types was placed into one of four risk categories: Critically Endangered, Endangered, Vulnerable, or Least concern. Critically endangered, endangered, and vulnerable are collectively referred to as the threatened categories.

Technical documentation

Code repository

Skowno, A.L. 2025. SANBI-NBA Wetland ecosystem threat status [Source code]. GitHub repository available at https://github.com/askowno/RLE_riv

Key publications

Harris, L.R., Skowno, A.L., Holness, S.D., Sink, K.J., van Niekerk, L., van Deventer, H., Smith-Adao, L., Job, N., Khatieb, S., Monyeki, M. (in review). Indicators for tracking progress in effective, representative ecosystem protection.