The transparency or clarity of Upper Saranac lake has exhibited a significant downward trend since 1993 in both the north and south basins. With a decrease in phosphorus and algal biomass in the lake surface, we would expect to see an overall increase in water transparency; however, this has not been the case.
Most recent Secchi disk transparency readings in the north basin ranged from 2.2 to 3.5 meters and averaged 2.6 meters. In the south basin, transparency was slightly higher and ranged from 2.6 to 3.7 meters with an average of 3.1 meters.
Transparency is a measure of water clarity in lakes. It is measured by lowering a 20 cm black and white disk (Secchi disk) to the depth where it is no longer visible from the surface. The transparency of a lake is influenced by many factors, including algal abundance, turbidity, suspended sediments, and dissolved organic matter.
Transparency can serve as an important indicator of the overall trophic condition of a lake as well as influencing human perception of water quality. In general, lakes that have low productivity and low algal abundance have greater Secchi transparencies. As algal productivity in-creases Secchi depths become much shallower. Transparency can also be influenced by the amount of dissolved organic material in the water. Dissolved organic matter rapidly attenuates light, resulting in lower transparencies.
Current research supports that decreasing transparencies in lakes is related to increased concentrations of dissolved organic carbon (DOC) (Williamson et al 2014. Montieth et al 2007). DOC has a strong ability to absorb light, thus when a lake becomes enriched with DOC, the transparency of the lake decreases. The primary source of DOC is decomposition in the terrestrial landscape. Warmer and wetter climatic patterns may be increasing the decomposition rate and flushing a greater pool of DOC to receiving lakes (Tranvik et al. 2009, Curtis and Schindler 1997). Increased DOC may also be a signal of recovery from acid deposition. As lakes acidify they tend to exhibit an increase in transparency due to a decrease in DOC (Yan 1983; Schindler et al. 1996), so it is possible that acidification recovery may result in an opposite effect.
For the most recent USF water quality update: https://usfoundation.net/programs/water-quality/