Veliger Sampling

Three times in the open water season, at locations strategically identified by the Sauk River Watershed District, volunteers help to monitor the various lakes in the watershed for veligers...the microscopic young of zebra mussels.

TOP LEFT: The nets, called "plankton nets" are dropped to just above the bottom of the lake at each of the identified locations. In Sauk Lake, there are 5 locations north of the bridge, and 3 locations south of the bridge.

TOP MIDDLE: Drawing the nets up, everything floating will be caught in the net and will drop down into the collection cup at the bottom.

TOP RIGHT: All of the water is vigorously shaken out through filters on the sides of the collection cup.

BOTTOM LEFT: That which is left, is transferred to a specimen container, preserved with 99% alcohol, and delivered to the proper folks to do testing for the existence of "veligers".

Thus far, though zebra mussels exist upstream in the Sauk River watershed (Osakis, Guernsey) and downstream (Birch and Lake Sylvia) they have not been discovered in Big Sauk Lake.

Secchi Disk Reading

There are many opportunities to contribute to making Big Sauk Lake the best it can be. One way is to participate in the Volunteer Water Monitoring program. Two of your Big Sauk Lake Association board members are helping with this and have been doing so for a number of years.

Jeff Mayer and Vern Beckermann take periodic readings at the locations specified on the map below. Under the map, you can see some good information that explains what a secchi disk is, where it came from, and some variations.

The links below will bring you to the MPCA data summary for the main bays of Sauk Lake. It looks like secchi disk data collection on Sauk Lake started in 1972 in one bay and 1980 in the other.



A Secchi disk is a circular metal plate attached to a calibrated rope. It is probably the most inexpensive and easy to use tool in water quality monitoring. One of the best aspects of the Secchi disk is that the information provided by the Secchi disk is easily interpreted by volunteers and can be used to detect water quality trends in lakes.

The Secchi disk is named after Fr. Pietro Angelo Secchi, scientific advisor to the Pope and astrophysicist. Secchi was asked by Commander Cialdi, head of the Papal Navy, to measure the transparency in the Mediterranean Sea. The first disk was lowered from the papal yacht, l'immacolata Concezion (Immaculate Conception), on April 20, 1865 (Carlson and Simpson, 1996).

Secchi disk color and style varieties

There have been many revisions to the first disks used by Secchi in terms of size and color. The two most common colors variations in use today are the all-white disk and black-and-white-quadrant version. In Minnesota, we use an all-white, 8-inch-diameter metal disk with notched sides for rope storage when the disk is not in use.