The Secchi Dip-In

The Secchi Dip-In demonstrates that volunteers can collect quality data over an entire continent. Since the Dip-In began in 1994 in six Midwest states, it has expanded to participation by more than 375 programs and 6,000 volunteers in the U.S., Canada, and several other countries. The Dip-In has generated tens of thousands of water transparency records that are used to map regional differences in transparency and to detect trends in transparency.

Volunteers that participate in the Dip-In routinely monitor all types of waterbodies, including lakes, streams, and estuaries, as a part of their normal monitoring program. Water transparency is affected by the color of the water and by particles of silt or clay or small plants called algae, and therefore is a measure of some forms of pollution.

Although the Dip-In accepts data from all types of turbidity instruments, most volunteers will use an instrument called a "Secchi disk," a flat, horizontal, black and white disk that is lowered from a rope into the water until it disappears. The disk itself is named after the Jesuit priest, Pietro Angelo Secchi, who used the disk more than 150 years ago. The depth the disk disappears is a measure of the transparency of the water.

The previous Dip-In events have provided valuable information about transparency. Maps of transparency show considerable regional differences in transparency. Lakes in the northern parts of the United States and in Canada typically have the greatest clarity, while lakes in agricultural regions of the Midwest have some of the lowest transparencies. Transparencies found during the Dip-In range from one inch to more than 65 feet.

Equally valuable has been the information gleaned on the volunteer's perception of water quality. The Dip-In has found that opinions of water quality vary considerably from region to region. A person in Minnesota, Maine or Canada, for example, may think that a lake is degraded if the transparency is six feet while in other states, a lake with a transparency of only a foot may be considered beautiful. Carlson suggests that these regional differences mean that people become accustomed to the quality that they see every day. Most sobering may be the possibility that everyone grows up thinking that their environment is normal. Small changes in water quality may go unnoticed. Fortunately, there are volunteer monitors who record these changes in water quality year after year. Without their observations, our environment might change unnoticed.

The volunteers have also changed our perception of what is considered to be a water quality problem. Typically, those who study lakes think of problems as algal scums and weeds. Although the volunteers think these biological nuisances are important, a group of human-related problems are also being found. Volunteers report that noise, boat congestion, rude boaters, and trash are also important water quality problems. In some states personal watercraft now equal or surpass algae and weeds as the chief perceived water quality problem. The volunteers' perceptions may not reflect the attitudes of all users of our waters, but they do remind us that aesthetics and human interactions are an important part of our environmental consciousness.

Monitoring programs and individuals are encouraged to use the Dip-In as a midsummer event to draw attention to their monitoring efforts. Various programs have had governors, federal and state representatives, and local officials participate.

More information on the Great American Secchi Dip-In, including participating programs and state-by-state results for past Dip-Ins, is available on the World Wide Web at: