Waterways

Hobart's rivulets are steep, rocky, freshwater ecosystems with pools and riffles, where fast flowing water moves over and around shallower, rocky areas.

The steep terrain has resulted in many small waterfalls and the shape of the landscape gives each rivulet just a short run before it enters the timtumili minanya/River Derwent.

In natural areas forest, including wet temperate rainforest, provides plenty of shading for the rivulets. The abundance of surrounding forest results in plenty of leaf litter and woody debris, which creates an abundance of different habitats for the organisms that live in Hobart's rivulets.

Typically, leaf litter and sticks washed down from surrounding forest would provide food and habitat for aquatic life in Hobart's rivulets. There would be relatively few plants and algae living within the rivulet system due to low light levels and the relatively fast flowing nature of these waterways.

A wide variety of animals make their home in Hobart's rivulets, including:

• platypus
• rakali (water rats)
• several species of jollytail (Galaxias spp.)
• wide diversity of waterbugs (also known as freshwater macroinvertebrates).

In an urban waterway, everything from habitat to water quality tends to be modified.

In areas with lots of infrastructure, waterways tend to be managed to minimise the risk of flood damage on nearby structures – roads, houses, buildings. These modifications change and limit the habitats available in a waterway and usually reduce the diversity of aquatic wildlife, including native fish and waterbugs.

• Urban waterways are characterised by much faster flowing water systems.
• Concrete and tarmac shed rainwater swiftly, and stormwater systems are designed to remove standing water as quickly as possible.
• Faster moving water often makes urban rivulets highly erosive places – channels are forced to move larger amounts of faster water than if the water was allowed to percolate into the soil across a catchment. This additional hydraulic stress often damages aquatic habitat by scouring, smothering or eroding sediment as water moves swiftly through the rivulet.

In 2023 the City of Hobart released its first ever State of our Rivulets report, which uses scientific sampling of waterbugs along Hobart's four key rivulets to measure the health of the city's inland waterways.

Waterbugs provide insight into the longer-term effects of water quality on the health of a freshwater ecosystem.

Waterbugs break down and feed on organic matter and each other. They are important food for larger animals in the food chain, such as native freshwater fish and the much-loved platypus, which inhabit Hobart's rivulets.

The diversity of waterbugs at particular points along a waterway can tell us much about that waterway's long-term exposure to impacts such as pollution and sediment.

The presence of more sensitive waterbugs indicates lesser impacts, whereas sites populated only by "tolerant" organisms suggest impacts of pollution, sedimentation and erosion. Tolerant waterbugs are those that have resilience to these impacts.

The upper reaches of Hobart's rivulets are excellent reference sites for what healthy local waterways should look like in terms of stream biodiversity and water quality when pollution is low to non-existent.

These upper reaches also act as a "biodiversity bank" by allowing sensitive waterbugs such as stoneflies and mayflies to breed and migrate downstream when conditions allow.

By measuring the ecological health of Hobart's four main rivulets over time through the presence of waterbug diversity, the City of Hobart can determine which areas most need closer monitoring and remediation.

The world of waterbugs is completely alien to most people, but for those willing to explore this miniature aquatic kingdom it is full of mystery, wonder and some of the strangest creatures on the planet.

In Hobart freshwater macroinvertebrates inhabit the city's streams and rivulets and are being used to measure the ecolgocial health of our inland waterways.

Mountain shrimp

Mountain shrimp live in the pools of the Hobart Rivulet just above Strickland Falls. They are more common in rivulets higher up the slopes of kunanyi/Mt Wellington.

These animals have barely changed their form since the Carboniferous period, 300 million years ago. They were described from fossils before the first living examples were discovered in Hobart in 1893.

Photo: Copyright © John Gooderham & Edward Tsyrlin

U-sthenid stonefly 

As a nymph, these insects terrorise the rest of the waterbug world in Hobart's rivulets. They hunt at dawn and dusk, moving around and under rocks and woody debris, running down sideswimmers and mayflies just as they are turning in for the night.

This waterbug lives as a nymph for a couple of years before emerging as a fully-fledged stonefly to look for a mate. They are quite common along walking tracks of our rivulets between November and June. When startled or threatened the adult stonefly flares up, showing its red hind wing.

Photo: Daniel Rhodes

Cow shrimp

Cow shrimp are the stars of Lambert Rivulet, where for some reason they are more common than in other rivulets. They live in the leaf litter that accumulates behind cobbles in the rivulet.

Cow shrimp are slow-moving, but well armoured, like miniature armadillos.

Photo: Copyright © John Gooderham & Edward Tsyrlin

Sideswimmers

Sideswimmers can grow to the size of a 5 cent piece. Their body is flat, allowing them to slot between cobbles and leaves, which they shred to bits while feeding.

These are the most numerous waterbugs in the upper parts of Hobart Rivulet and are likely an important food source for platypus.

Photo: Copyright © John Gooderham & Edward Tsyrlin

Log cabin caddis

Many caddis are master builders, the larvae create protective structures from materials at hand – sand grains, silk, or in the case of the log cabin caddis, freshly-cut water weed lumber.

The structures caddis build are completely mobile, allowing the caddis to move around underwater in their own mobile mini-home.

Photo: Copyright © John Gooderham & Edward Tsyrlin

Tinsel-gilled mayfly

There are many mayfly species in Hobart's rivulets.

The tinsel-gilled mayfly has distinctively fluffy gills along its abdomen. Absence of mayflies indicates pollution in our waterways, which is why they are the mascot for the National Waterbug Blitz.

Photo: Copyright © John Gooderham & Edward Tsyrlin

Hobart's rivulets are home to a wonderful range of aquatic wildlife, including native fish, the rakali – a native rat, and of course platypuses.

But while Hobart's rivulets are ecologically healthy and well protected within the forests of Wellington Park they face multiple challenges as they enter Hobart's suburbs and the city, including rubbish and pollution.

Discarded twine has led to the death of a platypus in the Hobart Rivulet.

Help keep our platypuses safe

• Pick up litter – particularly anything that could get caught around a platypus's bill, neck or body – whether or not the litter is found near water.
• Spread the word that plastic bracelets and elastic hair ties can be lethal for wildlife. Items dropped in the street or in playgrounds can be carried through storm water drains and into platypus habitat.
• If you see a platypus in distress please avoid trying to contain or handle the platypus. Males have venomous spurs on their hind legs that can cause excruciating pain. Keep pets away from the platypus, try to maintain sight of the animal if possible, and call the Bonorong Rescue Service on 0447 264 625 (0447 ANIMAL) for further advice.
• Cut through ALL metal or plastic rings or loops of any size before disposing of them – just to be on the safe side.
• Avoid washing motor vehicles on impermeable surfaces such as driveways or carparks, especially if the soapy water runs off to a concrete gutter or stormwater drain.
• Minimise your use of herbicides, pesticides and fertilisers on gardens.
• Avoid disposing of household chemicals (lubricants, solvents, preservatives, cleansers, paints, etc) by pouring them down a gutter, drain or toilet – instead, consult your local council's website to find out how to safely dispose of chemicals in an environmentally friendly manner.
• If you see pollution in or entering Hobart's waterways please report it to the City of Hobart Customer Service Centre on 03 6238 2711. This includes not just paint, but sediment from building sites and concrete wash.

Get active for nature

Get involved with the City of Hobart Bushcare program. The Hobart Rivulet Bushcare group is our newest and doing great work enhancing platypus habitat along the rivulet.

To find out how to get involved visit our Bushcare page:

Bushcare

Become a citizen scientist

People across Australia are joining the citizen scientist movement and becoming active participants in monitoring and tracking the health of our native species across.

You can do that too by helping scientists discover more about the behaviour and locations of Hobart's platypus populations by reporting sightings using a number of apps:

• iNaturalist
• The platy-project
• Austalian Platypus Conservancy