Lake Maintenance

This page addresses the practices used to maintain Rainbow Lake (also known as "the pond") prior to its expansion in 2008 to about 3.2 acres and about 20 feet deep. For information on expanding the lake see the Owners Only section (password required).

Description

Rainbow Lake is (i.e. was until 2008) a long 2.1 acre body of water that abuts Lots 3 thru 7 and surrounds two islands. Maximum depth is 8.5 feet and much of the pond is much more shallow. The pond is fed by groundwater seepage and is topped up approximately three feet above the water table from the well near the schoolhouse. The elevation of the water surface is 4,165 feet above sea level. There is no outlet except seepage through the ground.

The lake is stocked with rainbow trout in May and some trout survive over the winter.

Water Intake

A pipe from the well house near the school runs down the pedestrian right-of-way between Lots 2 and 3 and delivers water at three valve-controlled points along the west side of the pond. The pump is 15 horsepower and rated at 300 gallons per minute (though the pipe limits the flow to less than 300 gpm). The pressure at the wellhead is 450-500 psi. We believe the pipe from the well is steel because PVC is not rated to handle pressure this high.

The well pump runs on a timer for about four hours a day. The ranch foreman runs the pump for extra hours when the lake gets low and may shut it off during the spring snow melt when the water table is almost at the surface of the ground.

Chemistry

Tested in September of 2007, the pond chemistry is good for trout. While the pH is higher than ideal (8.19 parts per million found versus 6.5 to 7.5 desired) the alkalinity of the water (78 ppm), which measures the "intensity" of the pH indicates that the pH is not a problem. Phosphorous, which contributes to the growth of algae and weeds, is at 0.127 ppm - relatively low for a residential environment. The water is chemically safe to drink but was not tested for bacteria that could make it unsafe to drink. See the report on pond chemistry in the Owners Only section of the web site.

Algae and Weeds

Weeds and algae sometimes make the pond less attractive and interfere with fly fishing by snarling lines. In 2007 the ranch had Aquacide evaluate samples of the weeds and algae in the pond. They identified three types of weed as follows:

1. Milfoil looks like groves of trees underwater. It has many leaves/branches off each main stem but the main stem doesn’t branch into multiple stems.
2. Sago Pondweed is the long stringy weed with long narrow leaves.
3. Duckweed is the small floating leaf that looks like a four-leaf clover.

Aquacide also identified the two types of algae: Filamentous Algae and Chara.

The algae and duckweed grow quickly and are most detrimental to the appearance of the pond. The milfoil and sago pondweed grow more slowly and snag fishing lines and hooks in addition to being unsightly.

Algae and Weed Treatment

The ranch uses its rowboat and a tank with a battery-driven pump to spray the pond for algae and weeds (see photos below). The ranch chooses to treat them separately because the algae is close to the shore and the weeds are more evenly distributed. The ranch chooses to kill only some of the weeds in order to provide habitat for the aquatic animals that fish eat and to avoid a sudden massive decomposition of dead weeds that would rob the water of oxygen the fish need for respiration.

Treatment requires one person to row the boat and one to manage the sprayer. Treatment must be done on calm days because wind disperses the spray and can make the boat hard to control.

For algae the ranch uses four gallons of Cutrine-Plus liquid approximately four times per year for a total material cost of about $700. The ranch plans to experiment with a product called called Cide-Kick II that should make the Cutrine-Plus go further and be more effective.

For weeds the ranch uses diquat dibromide (brand name Reward, also sold as Weedtrine-D) about two or three times per year for a total material cost of about $400. Removing all the weeds would increase the cost.

The ranch foreman rakes out the weeds and algae after killing them so their decomposition doesn't rob the water of oxygen and so that the dead plant material does not provide nutrients for more algae and weeds to grow.

Possibly More Effective Treatment

The ranch received a proposal from Aquatechnex, who manages the golf course ponds at Crosswater, to treat the current pond for about $7,000 per year. They could kill everything and make the pond as clear as a swimming pool if that is what we want. The biggest change from current treatment would be to apply a product called Sonar in April or May, just as the weeds start to grow. Over a period of a month Sonar will kill every plant that grows in the water, including the reeds and cattails. Aquatechnex would also treat periodically with Cutrine-Plus and diquat. The ranch could continue with Aquatechnex every year or could take over treatment itself.

The Sonar for one treatment would cost $1,400 to $2,100 if the ranch applied the product itself.

Lake Maintenance Photos