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Diamond Lake is an important recreational and residential lake located six miles south west of Newport. The lake is 750-acres and has good water quality. Eurasian watermilfoil (Myriophyllum spicatum) has been present in the lake since 1998 and efforts to contain/eradicate the infestation have been ongoing. Diamond Lake supports significant public recreational uses such as fishing, swimming, boating, skiing, personal water craft, nature observation, and aesthetic enjoyment. There is a public boat launch operated by the Washington Department of Fish and Wildlife and a private resort. The Boy Scouts own over 6,000 feet of shoreline. Their camp and property is used extensively for education, training, and enjoyment and they will be severely affected if milfoil is left unchecked.
The goal of this project is to eradicate/contain the extent of the infestation in Diamond Lake using selective aquatic herbicides to reduce the size of the current infestation and following up using diver hand removal and an extraction vessel to facilitate plant disposal. The Diamond Lake Improvement Association is an active and involved group has built the extraction vessel.
Diamond Lake was treated with 2,4-D (AquaKleen) on July 11, 2003. It was applied using a granular blower at a rate of 100 pounds per acres by a licensed applicator. A total of 13.75 acres were treated at scattered locations around the littoral zone of the lake. Surface samples were collected from inside and 100 m. outside of three treated areas by a Diamond Lake resident. The lake was also treated with AquaKleen on September 4, 2003 with a total of 8.75 acres treated in September. Surface samples were also collected from inside and 100 meters outside of three treated areas by a Diamond Lake resident. All samples were analyzed by an Ecology- accredited laboratory using USEPA method number 8151A.
Diamond Lake was visually surveyed by boat on August 4, 2003 and the treatment efficacy was rated at about 70 percent for milfoil control after the July treatment. The lake was surveyed again on September 26, 2003 and the efficacy was rated at 90 percent for milfoil control.
Only one 2,4-D sample was above the EPA drinking water standard of 70 ppb at 24 hours.
Treatment Site 1- July Treatment: South side of Lake (approximately 3 acres treated in a deeper site (5-10 feet)
| Time | Inside the Treatment Site | 100 meters Outside the Treatment Site |
| 1 day after treatment | 3.4 ppb | 2.5 ppb |
| 3 days after treatment | 3.4 ppb | 2.1 ppb |
Treatment Site 2 - July Treatment: Northwest side of Lake
(approximately 5 acres treated in a shallow site (2-3 feet)
| Time | Inside the Treatment Site | 100 meters Outside the Treatment Site |
| 1 day after treatment | 44.3 ppb | 17.1 ppb |
| 3 days after treatment | 52.9 ppb | 57.9 ppb |
Treatment Site 3 - July Treatment: North side of Lake (Scott
Bay) (approximately 0.25 acres treated) (deeper site)
| Time | Inside the Treatment Site | 100 meters Outside the Treatment Site |
| 1 day after treatment | 1.9 ppb | 1.1 ppb |
| 3 days after treatment | 4.2 ppb | 2.6 ppb |
Treatment Site 4 - July Treatment: Northeast side of Lake
(approximately 5 acres treated)
| Time | Inside the Treatment Site | 100 meters Outside the Treatment Site |
| 1 day after treatment | 17.6 ppb | 6.9 ppb |
| 3 days after treatment | 14.6 ppb | 20.1 ppb |
Treatment Site 4 - September Treatment: Northwest side of Lake (approximately 5 acres treated) (shallow site)
| Time | Inside the Treatment Site | 100 meters Outside the Treatment Site |
| 1 day after treatment | 72.4 ppb | 9.9 ppb |
| 3 days after treatment | 63.7 ppb | 5.5 ppb |
Treatment Site 6 - September Treatment - Northeast side of
Lake (approximately 2 acres treated) (shallow site)
| Time | Inside the Treatment Site | 100 meters Outside the Treatment Site |
| 1 day after treatment | 19.7 ppb | 21.4 ppb |
| 3 days after treatment | 25.13.4 ppb | 7.3 ppb |
Treatment Site 8 - September treatment - Southwest side of
Lake (approximately .25 acres treated) (deeper site)
| Time | Inside the Treatment Site | 100 meters Outside the Treatment Site |
| 1 day after treatment | 6.7 ppb | 3.1 ppb |
| 3 days after treatment | 7.0 ppb | 3.2 ppb |
Click here to see the sampling form for July (Word document)
Sampling form for September (Word document)
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