First, I'm not implying this information is guaranteed 100% correct. All are subject to change and I haven't confirmed any this year although the map of the Detroit River is up-to-date. Most have been accurate for a while now. As you found out, they don't necessarily let you get away with saying you don't know either.
Michigan water speed is 55mph statewide unless posted slower. No-wake is 100 ft within docks, swimmers, lake shoreline, boats that aren't running (fishing, anchored, sailboats, etc), divers. Technically, I believe there is a 100 foot no-wake buffer approaching a no-wake zone and leaving too. On the Great Lakes, the 55mhp speed limit only applies out to 1 mile from shore, then the speed is unlimited last I checked.
US no-wakes include CHANNELS - All Boats: the North Channel is No-wake from Chenal A Bout Rond (Sni) mouth to the buoy downstream past the last dwellings;
Sni has two no-wakes from 1) the mouth at North Channel downstream to the buoy just past the first set of dwellings (lot's of boats blow this one, but I always see the sheriff boat no-wake it - "when in Rome…" some people say this is the basic 200 foot for boats under 26 feet, but I have not asked the local sheriff patrol to confirm this);
2) way downstream near the end you'll see a buoy just before the small island houses (past Doty Highway, near Strawberry Island) which continues to another buoy past the last dwelling a few hundred yards before Fisher Bay (NOTE: the entire Sni Channel is no-wake to boats 26 feet and over);
off the Sni - Doty Highway near all the island houses, and Baltimore channel - both buoyed;
pretty much all the small side channels off the North, South and Middle Channels are no-wake if they have any kind of dwelling and/or docks since general Channel no-wake is 200 feet from shore for boats under 26 feet and 600 feet from shore for boats 26 feet and up - if you do have a big cruiser, you can run much of the North and South Channels, but can be ticketed if running much of the Middle Channel anywhere there are dwellings even though this is still a big channel;
LAKE: Clinton River has buoys out front and all the river inside the harbor in is no-wake and this wake is enforced at a very low tolerance level and easy to find out what it is since the sheriff station has deputies constantly watching the heavy boat traffic in there;
Black Creek (Metro Park) is the same as Clinton River ;
Off limits way back in for the beach at the Metro Park south of Point Huron and a jet-ski area I keep hearing about, but I never go that far back into that corner, but I believe it's all buoyed off;
No-wake out from all the marinas near the 9 Mile apartment tower (the nautical mile) - I believe there is a Macomb County ordinance for that whole area from just South of Bayview Drive (~ ½ mile South of 11 Mile Road (The Blue Sea Wall) to Gaukler's Point covering a 600 foot no-wake - the area right out in front of the marinas has buoys, the rest doesn't, but I rarely run in close to this area so I have not gotten specifics on this ordinance, I just know boat traffic is extremely heavy here on a weekend making fishing the '9 Mile' bar very 'exciting' for anyone in anything smaller than a missile frigate.
The Canadian side is shrouded in mystery - okay, not really, but I believe, based on my translations from Canadian to English (ay) and metric to US, that they have a general 100 foot rule around the entire lake and channels unless posted otherwise. Most of the larger Ontario side channels (Ecarte) in the St. Clair River and over in Mitchells Bay are posted, usually 5 kph (which I take to be kilometers - slow - unless it says knots), watch for the signs and don't get caught running them. It's been a while, but I believe the Thames River is 5 kph too. Definitely any of the smaller tribs on the South shore are no-wake.
Walpole Indian Reservation channels fluctuate. Lately, the entire Bassett channel has been no-wake and off limits to jets skiers, but I see both things occur all the time. I don't fish it anymore (other than the mouth) because I won't run it if the signs are up. The Johnston has been posted some years and not in others. I haven't been there in a couple years so I don't know the present state, but I believe there is a no wake in the mouth area and another stretch way up the channel. The Chematogan is no-wake from the mouth off the South Channel down past the 'Chief's House' where there is a sign at that end of the no-wake. Last I knew, the rest of the Chematogan is runnable (no jet skis), but as I say, this is subject to change. They usually have large, clear signage.
The US side of the Detroit River is really complicated with a different ordinance every mile (it seems) and since I'm not a lawyer, I won't interpret them here, just stay as close to the middle of the shipping channel as you can and safety allows (you'll understand this fully if you ever 'run the Ambassadeur Bridge' on a weekend afternoon in anything smaller than a frigate. Some no-wakes down there are 1,000 feet from shore. Many side channels are entirely no-wake. Canada has some good sized side channels posted as 5 (~5.75mph) or 10 knots or kph which is plowing pretty good, but not running obviously.
Thanks Dan for the info. I guess my argument is out the window. I have been traveling that area for many many years and have never been approached concerning "NO WAKE". I would encourage all the fancy glitter boat owners to be especially aware to all the "MYSTERY" regs. out there, as I was informed by the sheriff it is "up to me" to know of all the posting's. Mind you everywhere else bouy's are evident. The fine for that area is $140. I wonder how they stop the wake from the tuna boats from going into those area's?