Local rivers are ecologically important, nurturing at least 400 species of aquatic and terrestrial vegetation, include algae, mosses, ferns and flowering plants. Regarding vertebrates: at least 120 species of freshwater fish, 20 species of frogs, 5 species of tortoises and several snakes have been recorded. There are also invertebrates such as crabs, shrimps, molluscs, and insects (such as dragonflies and stoneflies). Some of these species are of regional and global conservation significance, such as Ketupa zeylonensis and Lutra lutra.


Water Lettuce (Pistia stratiotes)

Rose Bitterling (Rhodeus ocellatus)
© Matthew Sin

Hong Kong Paradise Fish (Macropodus hongkongensis) is unique to Hong Kong

Gunther's Frog (Hylarana guentheri)

Reeve's Terrapin (Chinemys reevesii)

Marsh Skimmer (Orthetrum luzonicum)

Adult stonefly


Japanese Mitten Crab (Eriocheir japonica)

Water penny (beetle larvae)
The upper courses of many Hong Kong rivers are within country parks, so are protected from development and damage by humans. As a result, the river channels and vegetation are well conserved. Common aquatic plants of the upper courses include Acorus tatarinowii, Horsetail (Equisetum spp.) and Pipewort (Eriocaulon spp.).

As the upstream channel is shallow and narrow, the water flow is rapid and flow volumes vary greatly, aquatic animals found here are usually small, such as Macrobrachium hainanense, mayfly larvae, and Hong Kong Newt (Paramesotriton hongkongensis).


Frail Horsetail (Equisetum debile)

Acorus tatarinowii

Macrobrachium hainanense

Hong Kong Newt (Paramesotriton hongkongensis) can only live in clear, unpolluted streams.

There are many benthic organisms in local rivers. Their diversity is the highest among local river organisms – with species including Rhinogobius duospilus, Striped Loach (Schistura fasciolatus) and Broken-band Hillstream Loach (Liniparhomaloptera disparis), exceeding the variety of free-swimming and floating organisms. This is because there is less sorting of alluvium along the upper course riverbed. Rocks, sand and gravels of various sizes create a complex benthic substratum, which suits different benthic species. Sorting of alluvium gradually improves downstream, with an increasing proportion of sand and mud, so biodiversity of benthic organisms is lower downstream.

The middle and lower courses of many local rivers are affected by pollution and development, so the species and distribution of aquatic species differ from those in natural rivers. For instance, water pollution downstream restricts the distribution of fish that are highly sensitive to dissolved oxygen levels, such as Predaceous Chub (Parazacco spilurus). But it favours species with high resistance to serious pollution, such as Mozambique Tilapia (Oreochromis mossambicus).

Upstream fish such as Striped Loach (Schistura fasciolatus) are mostly benthic.

Broken-band Hillstream Loach (Liniparhomaloptera disparis)

Predaceous Chub (Parazacco spilurus)

Mozambique Tilapia (Oreochromis mossambicus)

Human activities also alter the natural aquatic plant species of the middle and lower courses. The original vegetation may be replaced by other species that include crops such as Water Cress (Nasturtium officinale) and Ginger Lily (Hedychium coronarium), Napier Grass (Pennisetum purpureum), and weeds such as Primrose Willow (Ludwigia octovalvis), Common Day-flower (Commelina communis) and Cyperaceae spp.


Water Cress (Nasturtium officinale)

Primrose Willow (Ludwigia octovalvis)

Common Day-flower (Commelina communis)
Humans may also introduce exotic species into the middle and lower courses. Common exotic species include Pomacea lineata, Mozambique Tilapia (Oreochromis mossambicus) and Variable Platyfish (Xiphophorus variatus). With their high adaptability and few natural enemies, these compete with native species for resources including habitats and food. The original river ecosystem is highly compromised.



Pomacea lineata

Variable Platyfish (Xiphophorus variatus)



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