Experts told of `multiple stress' to Californian lake

Enthralled by its cobalt blue colour, Mark Twain described it as "the fairest sight the whole earth affords". However, unrelenting urbanisation around Lake Tahoe means the description may soon be only applicable to its past.

Situated between California and Nevada, the majestic lake is experiencing "multiple stress", according to Prof Charles Goldman, of the University of California, who has overseen 40 years of research on what was considered one of the great western lakes of the US.

The environmental throes it is now being subjected to should sound warning of the threat to many of the world's large lakes.

With California's affluence, "if we cannot resolve this environmental problem, it really bodes ill for the world as a whole", Prof Goldman told the limnologists' conference. The lesson for those with lake systems within their ambit was to "apply science to decision-making and development at an early stage".

He said the extent of unprecedented stress on lakes had to be responded to rapidly with a multidisciplinary approach. Very complex problems needed, for example, ecologists, hydrologists and civil engineers to work together.

Lake Tahoe's trees were denuded from its shores due to mining in the last century and while 100 years later they had returned, poor forestry policy meant that after one bad fire it would be back to the erosion of the past.

The Sierra Nevada's biggest wetland was lost in the late 1950s to a large marina. Unabated development in the 1960s and 1970s in the Tahoe basin compounded the problems. Wells became polluted with nitrates from septic tanks and groundwater became contaminated.

A development control agency was set up but the Californian authorities had to force the introduction of restrictions.

A "green margin" began to appear on its shores due to algal growth, leading to obnoxious smelling blooms. People began to realise the lake was changing from its usual crystal clearness.

The strain, nonetheless, was still evident with a decline in oxygen levels and nitrogen accumulations in the water which has become sensitive to discharges containing phosphorus. When he announced Lake Tahoe was subjected to smog, and could on occasion have an air quality not dissimilar to downtown Los Angeles, people were unwilling to accept it.

Equally, a fuel-use policy was having a disastrous impact on groundwater, said Prof Goldman. A jetski, for example, using a combination of oil and gasoline, discharged one gallon of unburned fuel into the lake for every five gallons it used.

Despite being subject to multiple stress, the lake was still in good condition. The legacy of a "less desirable environment" would, however, soon result if the response was not immediate and adequate.