Hi DougMo

Yes, you could be correct.

I don't know about depriving oxygen, but blooms can and do cause problems. You could ask your local fisheries or wildlife dept if they have any info on it.

YO DOUG MO ,DONT YA KNOW THAT TROUT(IM GUESSING THAT'S WHAT YER AFTER)IS A SCHOOLING fish & 90 PERCENT ARE IN 10 PERCENT OF THE LAKE ....ITS YOUR/OUR JOB TO FIND WHERE THEY ARE CURRENTLY AT. !!  IM HAVING A ROUGH TIME RIGHT NOW TOO.
A QUICK STORY..............A FEW YEARS BACK WE WERE KNOCKING THEM   D E A D  !!   FROM SUN UP TO SUN DOWN EVERY DAY ALL DAY,ALL SUMMER LONG (DIDNT MATTER -THE FISHING PREDICTION)....BUT AS SOON AS THE SUN WENT DOWN THEY WOULD  S T O P. !! BITING !! IT WAS CRAZY........YOU HAVE TO FIND THOSE SPOTS ON YER LAKE.!!...... PLEASE LET ME/US  KNOW WHEN YOU FIND THEM...........(I MEAN EVERYONE WAS CATCHING THEM THEY WERE ALSO FEEDING ON THE BABY BASS HATCH + GORGING THEMSELVES ON THEM....SEEMED LIKE THE WOULD BITE ON ANYTHING)