Clean healthy water is central to our whole ecosystem – it supports people, agriculture, animals and plants. In the Wet Tropics, we also depend on our waterways for our lifestyles and livelihoods. But these can also cause significant impacts.
The Wet Tropics is one of the six bioregions adjacent to the Great Barrier Reef where poor water quality runoff from land-based activities is one of the key issues affecting the health of the reef.
In recent years much of the effort to improve water quality has been focused on supporting farmers to reduce nitrogen, pesticides and sediment runoff. While progress is being made, it is not happening fast enough to meet the ambitious water quality targets set by the Government.
These include reducing nitrogen by up to 80% and sediment by up to 50% by 2025 in key catchments including the Wet Tropics.
The Wet Tropics is a hotspot for nitrogen (fertiliser) and pesticides due to the following:
- Intense periods of rainfall
- Short sharp river catchments
- Close proximity of the Reef to the coastline
Intensive horticultural industries along the coastline
What has been done so far?
Many community groups and organisations are already engaged in activities to improve the quality of water flowing off the land to the Reef. These are guided by the Wet Tropics Water Quality Improvement Plan.
In 2015 Terrain NRM (one of the Partnership’s members) released the new Wet Tropics Water Quality Improvement Plan (2015-2020) after extensive consultation with stakeholders in the region. The aim of this plan is to better manage our waterways to deal with expanding agriculture and urban development.
Regional Water Quality Improvement Plans (WQIPs) are part of the Queensland and Australian Government’s Reef 2050 Long-Term Sustainability Plan. Their purpose is to bring together the latest science, and identify targeted approaches to tackling water quality issues at a regional level.
The Wet Tropics Report Card complements the Water Quality Improvement Plan by providing scientific information to determine whether current strategies to improve waterway health are working and what can be done to improve them.
For more information on the Wet Tropics Water Quality Improvement Plan, visit the Wet Tropics Plan for People and Country website.
aquatic pests and weeds.
Aquatic pests and weeds are plants and animals that are in the wrong place. Unfortunately, pests and weeds thrive in Wet Tropics conditions and this makes our waterways particularly vulnerable to aquatic pests and weeds escaping from ponds and aquariums.
The first records of aquatic weeds in the Wet Tropics show that they began to arrive in the 1800s. Most of the weeds we are dealing with today were introduced through the aquarium trade, as culinary plants, or were released for agriculture. The internet has made things worse by causing an explosion in food plants being imported from other parts of the world, especially south-east Asia.
In other parts of Australia, weeds die back during the dry months but because we have so much water all year round, weeds continue to spread. They can smother our rivers, alter their flow and change the water chemistry, which creates perfect conditions for pest species like tilapia to thrive. Weeds also have a negative impact on the productivity of our farms.
Pest fish compete with native fish for food, resources and habitat and, in some cases, they even prey on them. Some of the pest species that have made it into our rivers include tilapia, gambusia, platies, guppies and swordtails.
Tilapia is a particularly noxious species because it can reproduce so prolifically that it displaces whole fish communities. Tilapia was first reported in the Wet Tropics in the 1970s in the Barron River and there are now two species that have become naturalised in this catchment – the Mozambique Tilapia and the Spotted Tilapia. Tilapia have now been recorded in most of our Wet Tropics catchments.
What has been done so far?
Unfortunately, aquatic weeds are almost impossible to eradicate. The best we can do is control infestations as they crop up by removing weeds manually or with the use of herbicides. Community groups, rangers and parks services are among those involved in weed control programs. We can all help by making sure we don’t inadvertently transfer weeds to other areas via machinery and boats.
Some of the species that are affecting our waterways currently are water hyacinth, water lettuce, limnocharis, hymenachne and paragrass.
Recent surveys show that the Murray and Herbert catchments are the most impacted by invasive weeds in the Wet Tropics. Further north, the Barron River recently had an infestation of floating macrophyte Amazon frogbit (an aquarium plant), which has spread through several tributaries within the basin. On the upside, the Mossman River is looking better after two weed species, Salvinia and water hyacinth, were removed from known locations.
The Wet Tropics boasts some of the most diverse assemblages of freshwater and estuarine fish species in Australia, but the survival of many species is threatened by man-made barriers that prevent them from moving between freshwater streams and wetlands and the estuaries downstream.
Good connectivity, or “fish passage”, enables fish to migrate to and from breeding and spawning grounds, gives them access to deep water holes and wetlands for refuge in the dry season, enables them to respond to changing water quality such as dissolved oxygen levels, helps them find new areas for feeding, and also lets them evade predators.
It is estimated that there are thousands of fish barriers in the Wet Tropics, which prevent fish from moving between different habitats. This can mean there is less overall habitat available for fish to live in, which can lead to reduced fish populations. Barriers also impact fish diversity and disrupt lifecycles.
Unfortunately, invasive fish species like tilapia and gambusia can survive and reproduce in degraded and polluted waterways much more successfully than even our hardiest native fish species.
Enhancing waterway connectivity and health by removing barriers to fish movement is one way we can support native fish.
What has been done so far?
To better understand the risks posed by barriers to fish in our region, a number of projects and organisations are identifying the barriers and prioritising them for mitigation based on those that will give the best outcomes for our fish populations.
Experts use high resolution imagery and desktop analysis to identify the potential barriers. The top priorities are then physically investigated by a field team.
Factors including stream movement, flow rate, distance from the coast, physical specifications of barriers, and ease of modification are then considered, to work out which interventions will get the best ecological outcomes for fish while also being financially feasible.