You may have missed a report issued by the Texas Commission on Environmental Quality (TCEQ) on Dec. 23, 2019, because its title, “Trophic Classification of Texas Reservoirs,” didn’t exactly make headlines, even on Google.
But page four is an attention-grabber.
Canyon Lake is the second-clearest reservoir in the state, based on something called “highest mean Secchi disk transparency.”
International Amistad Reservoir ranked first at 4.6 m, followed by Canyon Lake (3.80 m), Brandy Branch Reservoir (3.38 m), Lake Alan Henry (3.24 m), and Lake Travis (3.06 m).
Reservoirs with the poorest light transparency are Rita Blanca Lake (0.06 m), Cox Lake (0.14 m), Palo Duro Reservoir (0.20 m), Lake Crook (0.24 m), and Lake Kickapoo (0.26 m).
To read the report in its entirety, click here.
Marty Otero, TCEQ media relations specialist, explains:
“One way the TCEQ evaluates reservoir condition is through the use of the Trophic State Index (TSI) which evaluates a reservoir’s nutritional status as indicated by measurements of nutrients, water clarity or transparency and algae in the water column. Assessing water body condition based on algae is accomplished by evaluating indicators that reflect nutrient dynamics that drive primary production and reduce transparency.
“The TSI provides a method for grouping reservoirs into discrete nutritional quality (trophic) states along a continuum from oligotrophic (poorly nourished-highest transparency-most clear) to hypereutrophic (over nourished-lowest transparency-least clear). One approach used to evaluate nutritional status is by measuring water transparency or clarity, determined using Secchi Depth.
“Secchi depth is measured in meters using a Secchi Disc, which is a device that is lowered into the water and the depth at which the disc is no longer visible represents the secchi depth.
“The TCEQ develops a report called the TSI Report to describe the condition and provide a ranking of the reservoirs in terms of nutrient enrichment and water clarity.