A search of Ebird records revealed much to my chagrin 😄 that my 7 grebes sighting was not the highest. The record is 13 .there were an abundance of records but I think I searched thoroughly.
The lucky 13 occurred January 22nd 2000
Several times a dozen grebess were reported: particularly in Nov 1998 from the 13th to 22nd.
Last week on the 12th Doug G also spotted 7. For accurate count it helps seeing them all together!