This figure shows the mean Secchi depth at site 1 from 1970 to 2006. Average secchi depth (m) is plotted on the Y axis, and date is on the X axis. As shown by the red trendline, there is a trend in decreasing mean Secchi depth. This change is most likely because of increases in algae growth as indicated by the historical chlorophyll data, which showed an increasing trend in chlorophyll-a concentration. The  transparency trend indicates that over the past two and a half decades, visibility and water quality have declined.