2004 Hideaway Lake Monitoring 

Description of the Site

Hideaway Lake is a shallow 18-acre waterbody located near the city of Rock Island in Douglas County, Washington that is heavily infested with Eurasian watermilfoil (Myriophyllum spicatum). Hideaway Lake has an average estimated depth of 6-8 feet and a maximum depth of 15 feet. The lakes of Rock Island were once sloughs left over from an oxbow of the Columbia River. In the 1970’s, a powerhouse was built at the Rock Island Dam which raised the water level causing the sloughs to increase by approximately six feet, creating larger lakes. Since the 90’s, Eurasian watermilfoil has been present in the lakes and in 2004 is so abundant that it poses safety concerns for swimmers, inhibits fishing and boating, negatively impacts fish and wildlife habitat, and has reduced the aesthetic appeal of the lakes. Hideaway Lake is used for remote-control boat racing, fishing, boating, and swimming, and has a habitat enhancement area and trail system along the southern shoreline.

The City of Rock Island Lake Enhancement Committee (LEC) was formed several years ago to address the issue of milfoil in these lakes. The City applied for and received a grant from the Department of Ecology to develop an Integrated Aquatic Vegetation Management Plan (IAVMP) for the Rock Island Lakes. The primary goal of the LEC was to control Eurasian watermilfoil. The aquatic herbicide 2,4-D was identified in the IAVMP as the control measure recommended for Hideaway Lake. The entire lake was recommended to be treated. In addition to the herbicide application, the LEC recommended stocking grass carp in this lake.


Hideaway Lake was treated with the liquid formulation of 2,4-D (DMA 4*IVM) by a licensed applicator on July 27, 2004. The herbicide was applied by subsurface injection at an application rate of 3 ppm and the entire lake was treated (18 acres). Surface water samples were taken by a water quality consultant in the middle of the lake prior to treatment and 3-days, 5-days and 10-days after application.  Samples were submitted to an Ecology-accredited laboratory and the samples were analyzed using EPA method number 8151A.

Hideaway Lake. The yellow area on the photograph indicates where the samples were taken.


Hideaway Lake was observed as the water samples were taken. Staff noticed a dramatic and immediate difference in the lake. Algae were also more apparent on the top of the lakes about 15 days after the application. This was partially due to the increased temperatures that occur in late July and August in eastern Washington. It was evident to staff that the herbicide application was effective in removing milfoil from the lake. Grass carp are due to be stocked next spring.

Summary of 2,4-D (DMA 4*IVM™) Residues

The 2,4-D treatment concentrations remained well above the drinking water standard of 70 ppb through the ten-day sampling period. The concentrations remained higher than those seen after DMA*IVM treatments in Lake Sacheen (2004) and Spring Lake (2003). However, only portions of these lakes were treated. Hideaway Lake was entirely treated with 2,4-D and this is probably why the 2,4-D concentrations were higher in this smaller lake. A recommendation for whole lake treatments in small, shallow lakes in the future would be to reduce the application rate to 1.5 ppm rather than 3 ppm as was used in Hideaway Lake. This should achieve excellent results and reduce herbicide use by half.  

Time After Treatment Middle of the Lake
Pre-Treatment Non Detect
1 Day after Treatment 1,320 ppb
5 Days after Treatment 1,240 ppb
10 Days after Treatment   675 ppb