Habitat requirements

Ideal habitat for platypuses includes permanent water, stable earthen banks consolidated by the roots of native riparian vegetation that is also overhanging the water, and an abundant supply of macroinvertebrates. Habitat features that promote abundant invertebrate prey such as riparian vegetation and complex in-stream structures including woody debris and cobbled substrates are also beneficial for platypuses. Conversely, any actions that remove or degrade these features will negatively impact platypuses. However, the relative impacts of both natural and human-induced environmental disturbances on platypus abundance, health and survival are poorly understood and requires more research.

Drought

Extended periods of low rainfall results in little available surface water. Smaller tributaries may dry up completely and larger streams can be reduced to a series of pools. This reduces the overall amount of habitat available for platypuses and fragments populations. Platypuses become more exposed to predation as they are forced to travel across land or areas of shallow water to find suitable habitat. Reduced flows can also affect the invertebrate prey of platypuses and impact riparian vegetation. The impacts of droughts are compounded by the removal of water by humans for domestic, industrial and agricultural use.

Clearing vegetation

Land clearing is a major threat to many Australian species as native vegetation is removed for urbanisation, agriculture or forestry. Native vegetation surrounding waterways confers a number of benefits including stabilisation of banks to allow burrow construction and reduce erosion. Unrestricted stock access to waterways causes further erosion of the banks. Bank erosion deposits fine sediments into the stream which clouds the water, reducing sunlight from penetrating the water and lowering overall primary productivity of the system. When combined with low flows, sediment can blanket the substrate, lowering habitat quality for benthic invertebrates and reducing available food for platypuses.

Overhanging foliage also provides cover from predators, shade over the water reduces evaporation and large fluctuations in water temperature during summer, and organic matter provides suitable habitat and food for macroinvertebrates. While introduced species can provide some of these benefits, it has been found that platypuses generally prefer native vegetation.

Modification of waterways

The relative scarcity of water in Australia places aquatic species like the platypus in direct competition with humans for this precious and limited resource. Humans frequently modify waterways by removing water and building dams and weirs which alters the aquatic ecosystem. Deep impoundments upstream of dams often provide poor habitat as platypuses preferably forage in water less than 3 meters deep. Water flow downstream of dams is generally greatly diminished, reducing available habitat, increasing in-stream sedimentation, and impacting the invertebrate community. The importance of environmental flows to mimic natural flow regimes in regulated waterways has only recently begun to be understood. Structures such as dams and weirs can also fragment populations by inhibiting movements along waterways. Although platypuses are known to leave the water to travel around such barriers, this significantly increases the risk of predation.

In contrast, some modifications such as appropriately designed artificial wetlands and shallow in-stream dams can provide excellent foraging habitat, particularly in degraded urban environments, as well as important refuge areas during droughts.

Predation

Like many Australian mammals, platypuses are vulnerable to predation by introduced predators such as foxes, dogs and cats. The impact of predation is increased during periods of low water and by structures that fragment habitat (dams and weirs) that force platypuses to leave the water to navigate their way around. Unsupervised domestic dogs around waterways are known to kill platypuses. Often the dogs are not acting aggressively, but merely trying to 'play' or investigate an unfamiliar object they may encounter in the water. Be aware that platypuses are not completely defenceless and the venom of an adult male platypus can be fatal to a large dog.

Netting

Opera house style nets are commonly used to catch yabbies and other freshwater crayfish. Unfortunately they can also be a death trap for platypuses and other air-breathing aquatic animals (e.g. water rats and turtles). Although illegal to use in public waters in Victoria, platypuses drowned by these nets are frequently reported, sometimes multiple animals in a single abandoned net. The platypuses are presumably attracted to the nets by yabbies already trapped inside but become stuck once they enter the net and quickly drown.

Litter

Platypuses can become entangled in discarded litter, fishing line, and mesh netting. Litter accumulates in waterways as it is blown or washed into the channel where it becomes trapped and washed downstream. The foraging behaviour of platypuses makes them susceptible to entanglement in any enclosed loops which can become stuck around their neck and front legs. This can impair swimming ability and therefore foraging efficiency, and if not removed can cut into the underlying skin causing severe injuries and death. Simple items such as rubber bands, plastic rings or hair ties can become lethal objects when discarded.

Poor water quality

Platypuses can be reasonably tolerant of poor water quality and have been found to inhabit quite degraded waterways, at least in the short term. However, changes to water pH, turbidity, temperature, and nutrients through urban, industrial and agricultural pollution can all indirectly impact platypuses by affecting their food supply/productivity.

Disease

There are few significant diseases known from wild platypus populations. In Tasmania, a small number of platypuses suffer from a fungal disease called mucormycosis. This potentially fatal disease results in skin lesions that can affect the animal's ability to forage efficiently and maintain its body temperature.  There has been no evidence of this disease on the mainland.