I know Middle River fairly well, or at least used too. I grew up there during the summers as my Grandpa was a member of Baltimore Yacht Club, and Commodore there back in the 80's. My Aunt & Uncle kept their Bristol 35.5 at Maryland Marina for many years, nice place. My best friend parents have kept their Morgan OI at Essex Marina since the early 80's. I sailed on their boats often out of Middle River as a kid. I kept my 24' Sea Ray at the marina (don't recall the name) just at the end of Martin State Airport for about 4 years.
I do not recall the airplanes dumping anything to speak of? Not saying it doesn't happen, but I have no proof it does either.
There are a lot of good deals to be had on Middle River. Bowley's Quarters is a nice resort/condo type marina. They were very helpful to me once after fueling up our new to us boat on one of our first outings. Essex Marina is about as protected as you can get, takes about 30 minutes of motoring to get to any sailable H2O. Rarely do you see jelly fish that far North, so if you're a swimmer that may matter? If I were to point out a couple of drawbacks of M/R it would be the intense amount of crabs pots that can be found at/near the mouth, and the fact that you really cant sail in the river unlike the Patapsco or Magothy for example, and on days like today that might be a choice one would like to have
Pros - Competitive rates, fresher water (ie swimming/ Hart & Miller Island), easy access to many great Northern Bay anchorages/creeks, good marina services,
Negatives - Allot of marinas = lots of boats, crab pot hell, noise from airport (not an issue for me, but some maybe?), cant sail much in the river itself (protected pretty well from a Southerly blow, but not so much from a Northerly one)
If I could find a place on the Magothy to keep the boat I would in a second! For now, Rock Creek off the Patapsco is it...and that ain't bad
PS, one thing I hate about Rock Creek/Patapsco...the pollution, it is the worst of the bay! Baltimore (sewage plants specifically) needs to clean up its act and get with the F'in program!