I would expect the anaerobic process to produce more of an orange matt like we get in caves. However, the water movement and quality is unique in caves.
If you do a search on Hydrogen Sulfide and fresh water- the reference to stratification comes up. Also Blue/ Green algae is another option.
Quote- an increase of ammonia, and the presence of hydrogen sulfide during the period of thermal stratification. Ammonia did not increase to a level considered to be toxic to aquatic species. It could, however, serve as a nutrient for certain species of plants and result in a change in community structure.
Link-
SpringerLink - Journal Article
Also LCRA makes the comment that the lakes turn over and this is a by product of that process.
Quote- When the lake turning process begins it often brings up bottom water that is very low in dissolved oxygen and high in hydrogen sulfide. You may notice a bad odor, like the smell of rotten eggs. This nasty odor is associated with this naturally occurring hydrogen sulfide, which is a gas that is dissolved in water. This hydrogen sulfide is formed from decomposing deposits of organic matter, such as decaying plant material. This odor will often remain until the lake waters slow their turning.
Link-
Trading places
For me its a basic sign of oxidation and stagnate water- yuck. I dont hang around.
The oil residue I find more worrisome- could it be run off or particulate in the water moving across the plastic?
If you guys are making regular visits take a page from the DIR playbook and ask LCRA if you could put in water sampling tubes and recover them on a regular basis.
You could also measure silt height, density, and water samples.
This would be great for extended range and training.
Thanks for all the work.
Regards, Andrew AKA Dangles
(joke from other thread.)
