The Green Lake of today is much improved from the pea-green scum, public closures, health risks, skin rashes and foul odors that characterized it in the summers of 2002 and 2003. Green Lake is blue again and seems to serve its citizens well as the most-used park in the state.

After a long history of attempts to maintain the lake, the city finally hit upon a winner: aluminum sulfate. A chemical commonly used to treat drinking water in many countries, aluminum sulfate, or alum, was first applied to the lake in 1991, in a very limited dose, and with very short-term effects. It wasn't until a more comprehensive dose was applied in 2004 that the green, odorous waters were cleared overnight, and the lake was reopened to its many users. At a cost of less than $1 million dollars every 10 years or so, or less than $100,000 a year, it appears that officials have found a miracle cure for the problems plaguing Green Lake.

However, while the waters of Green Lake are currently clear, its future management is murky. There is no budgetary assurance for continued alum treatments, and there are no plans currently in place for the environmental management of threats to Green Lake's continued viability: Eurasian watermilfoil, an invasive underwater plant, and European carp. A convoluted bureaucratic arrangement, involving a mixture of state government and city departments, is partly to blame. The result is a genuine lack of effort being directed toward a long-term environmentally and fiscally responsible program.

City Parks and Recreation Department spokesperson Dewey Potter said that an application to fund further treatments wouldn't be made until water monitoring indicated that conditions were worsening. This reactive management of Green Lake is the antithesis of good environmental and fiscal policy and repeats the trend that has failed to adequately solve any number of problems at the lake in the last 100 years.

The citizens of Seattle have been trying to keep clear the waters of Green Lake since the latter part of the 19th century. In 1911 the water level was lowered in a massive public works project to create more land for housing development. As Brittany Wright writes in Seattle's Green Lake, "A multitude of laborious efforts have been exerted since Green Lake's founding to halt its decay by treating its waters and dredging its sediments."

In the 1990s, the need to find a solution to the Green Lake problem reached crisis point. The lake was listed by the Department of Ecology as an impaired and threatened water body, and a succession of toxic algal blooms, promoted by an ecosystem starved of oxygen and overloaded with phosphorus, made it unusable and unsafe. In 2003 the Department of Ecology found that carp from Green Lake exceeded criteria for the protection of human health. Concerned locals formed Friends of Green Lake. Motivated by what they saw as insufficient management of such a heavily used resource, the group became the lake's only advocate. Members of the group monitored water quality, photographed the lake, and documented its changes. At their monthly meetings they studied the biology and ecology of the lake, and sought the advice of environmental experts. They also lobbied local government agencies to find a solution to the frequent algal blooms which render the lake unusable.

Algal blooms occur when the phosphorus level in the water gets too high. The phosphorus level builds up in Green Lake because there are no in and out flows, such as creeks and streams, to oxygenate the water and export excess nutrients. Phosphorus is produced by the decomposition of plant biomass, in this case Eurasian watermilfoil, and is encouraged by the rooting behavior of the European carp in the lake, which feed on bugs in the sediment. The droppings of birds and geese are also high in phosphorus. Other species of aquatic plants can help to oxygenate the ecosystem and combat phosphorus production, but they cannot succeed in Green Lake because the carp destabilize the sediment. The aluminum sulfate treatment is successful because alum molecules added to the water bind to the mobile phosphorus molecules and inactivate them, dragging them down into the sediment, where they are not able to fertilize the growth of algae.

The milfoil is a problem for boaters; it catches on props and oars. Its fragments clog the edges of the lake, decompose, produce that foul order, and increase phosphorus production. Efforts have been made in the past to harvest the milfoil with a machine — much like a cross between a hovercraft and a lawnmower. While this was effective in the short term, the milfoil simply grew back. A few years ago a team of divers went down to try to pull the milfoil out by hand, but the milfoil again grew back.

Ironically, there was only one thing that did have a sustained impact on the milfoil: the algae. When it covered the water surface, the milfoil was starved of sunlight. When the alum cleared the algae in 2004, the milfoil grew back.

"We need to establish a long-term lake management budget now," says Rob Zisette, aquatic science director of Herrera Environmental Consultants, the company contracted by the city in 2003 to study the undertaking of a comprehensive alum treatment. Their report was the blueprint for the successful 2004 treatment. Zisette has been involved with the management of Green Lake since 1991, and he is concerned that Green Lake is being managed on an ad hoc, reactive basis. Referring to the desperate state of the lake in the late 90s, Zisette says, "I am worried that we will just end up in the same place. We're almost half way through [the current alum treatment]. We need a long-term plan."

The complex, interconnected lake ecology demands appropriate planning and less reactive management of the lake, Zisette argues. The lake management plan currently in place was developed in the 1980s and has not been updated to reflect the problems and treatments of the past two decades.

Kevin Stoops, spokesperson for the Seattle Parks and Recreation Department, acknowledges that the carp and milfoil are elements that will continue to compromise the condition of the lake. Although no new methods are currently being explored by his department, Stoops says he is open to new ideas to solve the ongoing Green Lake quandary, should budgetary constraints free him to explore. "In a perfect world, I would like to re-evaluate and improve the storm drains along the southwest shoreline, and the drain from Woodland Park," Stoop says. "Perhaps these could be reworked to effect nutrient removal."

"We need more storm water control and treatment, but that's not going to be enough," says Zisette. "We need to do a lot of things, though alum treatment is the key. We may need more geese control, but that's not going to be enough. We may need to control the carp. We tried that, but actively there is now no carp management plan."

The European carp's presence has a devastating effect on other plant and animal species, and cities all around the world are experimenting with ways to get rid of them. Except Seattle.