I don’t know if it was a perch boil or a fish kill last week at the slip north of 87th Street.

Here’s what I know. I went there the next morning, April 5, after the photos went viral on Facebook the day before (and Mike Starcevich texted me some photos).

I’ve covered many fish kills. One to three things are almost always present after major kills: an odor or stench, something odd about the water (sheen, bad color, etc.) and/or unusual behavior by birds or animals.

The look of 87th Street slip on April 5, 2017.
Credit: Dale Bowman

None of that was present at 87th. No unusual odor. Water looked like it usually does. No gulls, just a couple hundred mergansers, which are often in the slip. Winds were east-northeast, nothing could have blown out.

So I checked the slip at 89th and Calumet Park. Gulls were notable at 95th, but not in unusual numbers (people feed the gulls there).

One of Chicago’s great photographers, Lloyd DeGrane, did the same trek shortly after me hoping to get photos for the Alliance for the Great Lakes. He extended it around to check the Indiana shoreline, too; and found nothing unusual.

Lake Michigan program manager Vic Santucci said veteran biologist Dan Makauskas checked the slip and found nothing.

Sgt. Jed Whitchurch had one of his Conservation Police Officers walk the entire slip. Nothing unusual was found.

“If there had been a fish kill, we would have seen thousands of shore birds,” Whitchurch noted.

“Hard to tell from a still picture, but until I get confirmation otherwise, I think it was a perch boil based on the location (in the slip where we have had numerous reports of this phenomena) and shape of the fish mass in the one picture (wedge shape with narrow end off shore a bit),” Santucci concluded.

Not sure who came up with the term “perch boil,” but it fits. I think Larry Jennings was the first to mention to me that perch boils were happening this winter at 87th.

Bruce Caruso took videos of a perch boil on Feb. 17 at 87th. He had three boils happen at three different spots that day. Others have taken photos and videos of perch boils at 87th.

A perch boil is what it sounds like, perch seeming to boil up by the hundreds or thousands to the surface.

“I believe those guys were seeing perch boils in the slips,” texted Carl Vizzone, whose family used to have two locations of Frank’s Live Bait & Sports (North Avenue and corner of Clark and Montrose). “It used to happen at Navy Pier back in the `80s when we had big perch populations. Good sign that they are rebounding.”

I consider Capt. Chuck Weis, who used to run Ace Perch Charters, the most innovative pursuer of perch on southern Lake Michigan. Saturday he gave me a theory, which is plausible enough that I intend to check it out over the next few weeks.

Some mysteries slide into the unsolvable.

TURKEY HUNTING: If good stories and photos come, I will run Turkey of the Week again.

WILD THINGS: Reports of morel mushrooms started Downstate late last week on morelmania.com. Remember, during spring turkey hunting at Illinois public sites open to turkey hunting, those areas are closed morel hunters and other visitors until 1 p.m.

STRAY CAST: Tom Skilling saying, “Backdoor Cold Front coming the lakefront,’’ thrills me as much as Matt Mullady saying, “Smallmouth are pounding topwaters on the Kankakee.’’