Update
I went back today and - from a distance - saw that the fountain was off..........and the maintenance lid was open.
The pool water was fairly clear (1) with a few tiny soapy remnants (with an inverted flag - 2). I spoke with the worker and found out that yesterday's soap geyser was not a wash/flush of the system, but rather a prank perpetrated very soon after the fountain was turned on for the first time this year - they didn't waste any time. He said that somebody dumped a bunch of (liquid?) soap and he was trying to clear the system of it. He drained the pool and refilled it (1), but when he turned the fountain back on, it was still somewhat soapy (3, 4). He indicated that he would probably have to repeat his efforts until the soap was gone.
Before I left, I noticed what appeared to be a liquid flagpole (5) and got a shot of the maximum height of the water (6).
As usual, click images for instant growth.