Mainstream monitoring is monitoring for the zebra mussel in any of its life stages, using the source water as the monitoring field. The source water is simply the body of water from which the facility draws (e.g., a lake, a large body of water, a stream or river). A variety of monitoring devices and sampling equipment are deployed to gather data on mussel abundance and the rates of dispersal, development, settling, and mortality. Both qualitative and quantitative data may be recorded depending upon the needs of the facility or site. Mainstream monitoring is most effective when used as an indicator for potential infestation to a facility. Because the monitoring devices are deployed throughout the source water, they give a good warning as to when a site may become infested.
It is important to note that while mainstream monitoring is a good way to detect and gather data on zebra mussels before they get to a location, it is not always 100-percent effective, i.e., does not always indicate the severity of the problem at a facility. An example of this occurred at the Detroit Edison Power Station, where bioboxes indicated zebra mussels were not in the area just before heavy zebra mussel encrustations destroyed the pump that provided water to the bioboxes and clogged raw-water lines throughout the power plant (Kovalak et al. 1993). However, with proper deployment techniques and adequate monitoring equipment, the use of bioboxes may be effective. If the site is extremely susceptible to mussel fouling, it may be a good idea to employ the Sidestream Monitoring system as well. More information mainstream monitoring techniques can be found in Claudi and Mackie (1994).
For information on which sampling gear and techniques may be most useful, see Monitoring Techniques.