Those eels are still present, but the water in the lake is now considered 'supertrophic', meaning it has unhealthily elevated levels of phosphorus and nitrogen, with the risk of outbreaks of botulism.
Auckland Council Parks and Places Team Leader David Barker says one major issue contributing to the lake's poor water quality is people feeding the swans, ducks and other water fowl in the water, rather than on land. Specific bird-feeding areas are proposed, along with increased riparian and emergent planting along the lake shore, to make the lake edge harder to access and discourage bread and other food from being thrown into the lake.
"What we want to do is educate people when they come to the park that feeding the birds this way can become a problem," he says. "If we can encourage people to feed the birds on platform areas out of the water, that will improve the issue."
Lake-edge planting will also reduce the amount of sediment entering into the lake, which also adds excess nutrients to the water, and filter stormwater runoff.
Barker says introduced pest fish such as koi carp, perch and tench are also an issue, as they are bottom-feeders which stir up sediment into the water, raising the nutrient level. The draft plan suggests eliminating exotic fish from the lake, allowing the native eels living there to thrive.
The management plan also proposes replacing a filter pond near the park's northern boundary with a natural wetland, again to improve the quality of water entering the lake system.
The Auckland Council's Healthy Waters team is currently carrying out water and sediment tests in Western Springs lake, using a remote-control boat to survey sediment at the bottom of the lake. Tests will be carried out once a month until April, with the results used to inform future decisions about improving water quality.
Barker says the plan that will be presented to the local board will reflect the feedback received from last year's public consultation. The plan also takes into account the park's heritage and cultural significance. Between 1874 and 1928 Western Springs lake was used as a source of drinking water for Auckland city and, during World War II, it was used as an American military base before opening as a park in 1977.
"We want to celebrate the past. We want to keep it as it is and not change the landscape, because people love it as it is. But there are some key areas we could improve," Barker says.
Significantly, however, when it comes to water quality Barker notes the issue is wider and more long-term than just making environmental changes at Western Springs.
"When looking at improving water quality, it's bigger than just the park. The lake is spring-fed, so we need to look at the wider catchment area and improvements to that go beyond the 10-year period proposed by this plan."
