Weed taking over lake in Tempe
By Dennis Welch, Tribune
August 3, 2005

An aquatic weed carried downstream by the recent monsoon storms is invading Tempe Town Lake and turning it green. The plant, known as duckweed, does not pose a public health threat. But unless the flow of water from the northern part of the state slows down, the green plant could become an enduring fixture on the lake, city officials said.

"This is something we may have to deal with for a long time," said Basil Boyd, a water resource hydrologist for Tempe.

The city plans to control the duckweed’s spread by using a special herbicide, but it was not known how much it will cost.

Boyd said they want to control the spread before it covers the entire surface of the lake.

While the green film on top of the lake may not look good to some, the plant does offer some benefits for the lake’s long-term health.

Boyd said duckweed keeps the algae population down because the two plants compete over the same food sources. But, in some parts of the country, duckweed has been reported to kill off fish populations by absorbing all of the oxygen.

Duckweed is a small plant that floats on the water’s surface, feeding off nitrogen and phosphorous and can double its biomass within 10 days, according to some reports.

Contact Dennis Welch by email, or phone (480) 898-6573