Pollutants are substances that negatively impact water quality. Some are naturally occurring but become pollutants when their concentrations increase above normal levels and become harmful to water quality and aquatic species.

In the Kanamaluka / Tamar estuary and catchment area, pollutants include nutrients (phosphorus and nitrogen), pathogens (enterococci), heavy metals, suspended solids, hydrocarbons, chemicals, and other contaminants. Pollutants can be transported into waterways through rainfall runoff (i.e. a diffuse source), or they can be directly discharged from a point source such as a sewage treatment plant or stormwater outfall.

Urban areas contribute a substantially higher pollutant load relative to their surface area due to higher population densities and the extent of impervious surfaces such as cement and asphalt, which prevents infiltration. Launceston’s combined sewage and stormwater system discharges a mix of sewage and urban stormwater into the estuary during high rainfall events, contributing to occasional nutrient and pathogen pollution. Upgrades are being made to the system as part of the River Health Action Plan.

Monthly water samples are tested for nutrient levels – that is, how much nitrogen and phosphorus is present. While nutrients are important, too much can be damaging to the ecosystem.

Both nitrogen and phosphorus encourage algal and aquatic plant growth which provides food for fish and other organisms. However, if nutrient levels are too high, excessive concentrations of algae can lead to algal blooms. Once algae die, the bacteria that consume them can use up all the oxygen in the water. This can severely impact the health of other organisms in the ecosystem.

Excess nutrients can enter waterways from the land, running off farmland and urban areas from animal waste and fertilisers, as well from sewage treatment plants.

Sediment is a naturally occurring solid material like sand, minerals, and organic matter that is broken down and can be moved to another location, usually by wind or water, but sometimes by ice too. Sedimentation is the process of sediment moving to a location and building up there, and is a natural process in the upper Kanamaluka / Tamar estuary.

Fine silts are carried in freshwater flows from the rivers in the catchment to the estuary. When fine silts meet the salty water in the estuary, the salt acts to clump sediment particles together through a process called flocculation. This causes the sediments to become heavier and to drop to the bottom of the water column.

Flood events can flush sediments downstream, but under normal tidal flows they tend to remain in the upper estuary. This is because the incoming tide is stronger than the outgoing tide, which acts to 'trap' sediments in the upper estuary. Over thousands of years, this process has formed the mudflats of the upper estuary, which are valuable habitat and feeding grounds for birds and other species.

Heavy metals are metals that have a relatively high density compared to water and are toxic even in small concentrations. Heavy metals can come from natural sources (like volcanic eruptions), however, their concentrations can be increased by human activities such as mining and metal smelting works.

The TEER Program monitors for heavy metals in the Kanamaluka / Tamar estuary each month, measuring concentrations of seven heavy metals including aluminium, arsenic, lead, cadmium, copper, and zinc.

Thankfully, since dredging and silt raking operations largely ceased in 2018/2019, the concentrations of dissolved metals within the estuary have generally remained low and have not significantly impacted water quality and ecosystem health.