The Secchi disk is a black and white plastic disk.  We lower it over the side of the boat and, using a viewing scope (pvc tube with glass on one end, helps to look down through the water), watch the disk descend.  The reading is the depth at which the disk disappears completely from view.  BPA began doing this work part way through the season in 1999.  Collected data from May through September every year.  We post the readings here for you to see.  In general, the readings seem to average around 20 feet, which is considered favorable when compared to similar ponds in Maine.

Clarity readings are an indication of soil erosion.  How?

If we have areas of exposed soil on the shores of the pond, or along the streams that lead to the pond, soil can be washed into Brettun’s Pond during rainstorms or when snow melts.  The soil carries phosphorous, which is a naturally-occurring ingredient of topsoil.  Phosphorous also happens to be the favorite food of algae, so when soil erodes into the pond, the algae get lots to eat, and then they multiply.  More algae in the water means the water is less clear, so our disc readings actually give us an idea of the concentration of algae in the pond.  If things truly got out of hand, meaning lots of phosphorous got into the pond, an ‘algae bloom’ may result.  This is something we don’t ever want to have happen in the pond.  Brettun’s Pond experienced algae blooms two years in a row back in the 1970s, but things have improved since then.

How Can I Help?

The number one way to keep Brettun’s Pond healthy is to look around your property for signs of soil erosion, and then do what you can to stop it.  Plant some grass seed or shrubs, place rocks to help slow down storm water runoff, etc.  Keep the soil (and pine needles, leaves, etc) out of the pond – that’s the best way to help.  Also, keep in mind that if you rake your property to get rid of old pine needles and leaves, you’re exposing lots of soil that may wash into the pond during the next storm.  Try to do your tidying up without exposing the soil, or take action to ensure that soil doesn’t get washed into the pond.  If you’re concerned about the amount of work you can do near the pond, contact the Code Enforcement Officer for the Town of Livermore by calling the Town Office.  You can also e-mail the officers of BPA using the addresses on the BPA Home Page.

Lower the disc, look through the scope, let your eyes adjust, and watch until the disc disappears completely.

Data has been collected from 2008 forward, thanks to Dennis Mancini and Dot Young.

Note 1:  Water sample collected on this date for DEP’s data set.  Results, as stated in the VLMP report for 2005:

Brettun’s Pond is a non-colored lake (average color 23 SPU) with an average Secchi Disk Transparency of 5.0meters (16.5 feet).  The range of water column total Phosphorous for Brettuns Pond is 7-12 parts per billion with an average of 8 ppb, while Chorophyll-a ranges from 0.9 – 11.9 ppb with an average of 4.6 ppb.  Recent dissolved oxygen (DO) profiles show moderate to high DO depletion in deep areas of the lake.  The potential for Total Phosphorous to leave the bottom sediments and become available to algae in the water column (internal loading) is moderate – high.  Oxygen levels below 5 ppm stress certain cold water fish, and a persistent loss of oxygen may eliminate or reduce habitat for sensitive cold water fish species.

(Note:  Brettuns Pond is considered by IFW to be a warm water fishery; it likely is not a natural native habitat for certain cold water fishes, although stocking efforts have made some cold water fish available to anglers.)