By D. A. (Midwested) on Wednesday, June 11, 2025 - 03:54 pm:
JT (and others),
Thank you for pointing this out, resulting in increasing my understanding. It would make for an interesting investigation to dig into the various Great Lakes vessels to discover which ones, if any, wait to discharge their gray water at shore-side (as they must do with black water) after moored at a destination.
Here is a link to the EPA regulations regarding the handling of gray water by vessels in U.S. waters.
I dug into it's 68 pages as much as my brain would allow. The only thing you stated that I wonder about is that urine might not be considered black water. Otherwise, it is all a bit disturbing.
I did find this short paragraph "carve out" on page 14 for the Great Lakes...
"3.3 GRAYWATER MANAGEMENT FOR COMMERCIAL VESSELS ON THE GREAT LAKES
Under CWA section 312, graywater discharges generated onboard commercial vessels operating on the Great Lakes must be treated through an MSD prior to discharge, or be held in on-board storage tanks and discharged to shore-side facilities."
An MSD is a Marine Sanitation Device. A Type II level is required for commercial vessels. Still, all it appears to do is treat for biologic pathogens, using chlorine, etc. It's not clear to me, at this point, regarding the possible chemicals (oil, detergents, etc) and heavy metals that probably would not be removed.