You almost certainly answered the question of why your water is brown in the last sentence of your post....CARP! Where there are common carp, I'd bet you also have bullhead catfish that are also rooting around on the bottom and suspending sediments into the water. Do a jar test to see if your water clears...Just get a sample of lake water in a clear glass jar, cover it, and let it sit undisturbed for 5 days...if some sediment sinks to the bottom of the jar, mechanical action is the cause of turbidity (wind/wave action or fish)....you can place a second sample jar in a dark closet for 5 days also...if rhe cause is an algae, it will die and either sink or float in the jar........The scum looks to just be a combination of protein slime from natural organis decay with lots of dust and pollen trapped in it...a decent rain will get rid of it
| 
