Waldo Lake, Oregon: Eutrophication of a Rare, Ultraoligotrophic, High-Mountain Lake

ABSTRACT

Waldo Lake, Oregon, was described in 1970 as one of the most oligotrophic lakes in the world. But limnological data collected since then indicate that the lake has shifted toward a higher trophic status. This finding is based on three sets of evidence: (1) the spectral distribution of downward irradiance has changed, with blue light now being attenuated more rapidly, while the penetration of both green light and red light has increased; (2) phytoplankton primary production rates have increased 20-fold; and (3) zooplankton have become many times more abundant, and species composition has changed entirely. Although the cause of limnological change is uncertain, investigators believe that it has resulted largely from management and use of the lake. Accordingly, lake visitors have increased dramatically over the past 30 years, from a few hundred visits in 1967 to around 170,000 visits in 1994. Moreover, stocking the lake with 20 million fish between 1938 and 1990 may have disrupted the lake's seemingly fragile ecosystem. Remedial action to save the lake is now being proposed, including (1) repair or removal of sewage-disposal facilities that are possibly defective; (2) tighter restrictions on various lake and watershed uses, and (3) a permanent ban on fish stocking.

Key Words:

• ultraoligotrophic lake
• high-mountain lake
• eutrophication
• lake remediation