Lake Argyle

Lake Argyle is a massive man-made reservoir located in the East Kimberley region of Western Australia.

It sits on the Kimberley Plateau, inland from the Joseph Bonaparte Gulf. The lake is positioned near the border with the Northern Territory and close to the town of Kununurra. As a huge body of water, it serves as the largest reservoir in Western Australia. It is also the second largest freshwater reservoir in Australia by volume. The lake was created by damming the Ord River, which serves as its primary inflow. Other water sources include the Bow River and various smaller creeks.

The creation of the lake involved the construction of the Ord River Dam. This project was completed in 1971 by the Dravo Corporation.

The dam features an earth-fill wall that is both long and high. Engineers consider this dam highly efficient. This efficiency is based on the ratio of the wall's size to the volume of water it stores. The lake was named after Argyle Downs, the property that the water partially submerged. During construction, a post office even opened at the site in 1969 to serve the workers.

Over time, the lake's capacity and structure have changed. In 1996, workers raised the spillway wall. This specific engineering change doubled the total capacity of the dam. The lake normally has a surface area of about 700 square kilometers. Its storage capacity to the top of the spillway is 19 million megalitres. At maximum flood levels, the water could cover 1,200 square kilometers. This high water level turns higher land areas into permanent islands. The lake's usual storage volume is about 17.3 million megalitres.

The reservoir is a central part of the Ord River Irrigation Scheme. This scheme was designed to use dam water to irrigate farmland in the East Kimberley. Originally, planners intended to grow rice crops for export to China. However, this plan failed because waterfowl, especially magpie geese, ate the rice shoots faster than they could be planted. While other crops are now grown, the lake is still considered Australia's most under-utilised lake.

The dam has also been recognized with a Historic Engineering Marker by Engineers Australia.

Damming the Ord River significantly altered the local environment. While river flows were reduced, a thriving new ecosystem developed within the lake. Lake Argyle and Lake Kununurra are protected under the Ramsar Convention. This international treaty recognizes them as important wetlands. The lake supports 26 species of native fish. These include barramundi, southern saratoga, archer fish, and mouth almighty. There is also a large population of freshwater crocodiles, estimated at 25,000 individuals. Some experts even debate if saltwater crocodiles are found there.

The surrounding mudflats and grasslands are an Important Bird Area (IBA). This area supports approximately 150,000 waterbirds. Twelve species are represented in numbers that are internationally significant. These include magpie geese, black-necked storks, and various plovers. The lake also hosts larger birds like the Australian pelican and the wedge-tailed eagle. Smaller birds such as the budgerigar and kookaburra are also common. However, the area faces threats from invasive species. Cane toads arrived in late 2008 and their numbers rose in 2009. Feral ungulates, which are hoofed animals, also pose a threat by over-grazing the shallow areas.

Lake Argyle connects complex systems of water, land, and biology. The management of sediment is one such connection. In the mid-1990s, sediment flowing into the dam caused concerns about losing capacity. By 2006, the continual regeneration of the upper Ord catchment helped reduce this inflow. The lake also connects to local industry, such as the Argyle mine. This mine operated from 1985 until November 2020. It was a major source of diamonds, yielding 865 million carats. Today, the lake remains a vital part of the Kimberley's geography and ecology.