BGF - I'm fairly certain that the surface-growth is
Variable-Leaf Pondweed and the submerged grass is southern naiad (Najas guadalupensis). If not Najas, the submerged mass could actually be a portion of the Variable-leaf Pondweed. Do the "two" plants appear to be connected (the same plant)?
The "best method" for controlling either/both (in August) isn't an easy call.
The control-method that poses the least amount of risk to your fish is manual removal. But, this will entail repetative efforts.
As for herbicides, AQUATHOL K might be the option that poses the least amount of risk - but low dissolved oxygen (DO) could still become an issue if the treatment it conducted too aggressively. On the other hand, poor weed-control results could result from an inadequate treatment approach.
Many variables come into play when formulating the appropriate level of treatment. Your pond's size, depth, water-temp, the presence of an effective aeration system, water-exchange, weed's population-level (% of coverage), etc, etc. If you want to elaborate on these variables, we might be able to give you better guidance.
It is far better to tackle aquatic "weed" problems before Aug - and before the plants become overpopulated.