North and South Twin Lakes suffer from poor growth and high mortality of stocked salmonids.  As a result of five years of study it was determined that the primary problem was that trout were limited to a narrow band of water during summer stratification because water temperatures in the epilimnion were too high and the hypolimnion was anoxic.  In 2008 a hypolimnetic oxygenation system was installed in North Twin and operated briefly.  In 2009 the oxygenation system was operated from mid May to Mid October.  Dissolved oxygen levels in the hypolimnion were kept between 5mg/l and 7mg/l.  Fish movements were monitored in both North Twin (oxygenated) and South Twin (unoxygenated as a control) throughout the summer by acoustic tracking, hydroacoustics and gill nets.  Fish were found to utilize the hypolimnion in North Twin but not in South Twin.

This project expands upon the initial study.  In 2010 North Twin Lake will again be oxygenated and South Twin will remain unoxygenated and used as a control.  Oxygen levels will be continually monitored in both lakes throughout the summer.  Numerous other water quality parameters will be measured in both lakes and fish movements, growth, condition factors and mortality will be tracked.

A hypolimnetic water oxygenation system will be constructed and tested in South Twin but it will only be operated long enough to ensure that it is working properly.  The oxygenation systems in both North and South Twin Lakes will be operated throughout the water stratification period in both lakes in 2011.