From an editorial published in the Toledo Blade:

"Western Lake Erie is too big to cor­rect its nox­ious al­gae prob­lem with large doses of alu­mi­num sul­fate, or alum, alone. Still, alum treat­ments ap­pear to be hav­ing at least a lim­ited pos­i­tive ef­fect on Grand Lake St. Marys.

At 12,500 acres, Grand Lake St. Marys is the larg­est open body of wa­ter in Ohio. Like Lake Erie, its rec­re­ational ac­tiv­i­ties are af­flicted by al­gae.
The state of Ohio has spent $8.5 mil­lion to ap­ply alum to 4,900 acres of Grand Lake St. Marys over the past two sum­mers. The com­pound is sup­posed to keep al­gae from feed­ing on its main food source, phos­pho­rus.
This year’s drought cut off the farm run­off that feeds Lake Erie al­gae. But al­gae in Grand Lake St. Marys rely more heav­ily on phos­pho­rus em­bed­ded in lake sed­i­ment, so this year’s dry con­di­tions did not do as much to curb al­gae there.
Pre­lim­i­nary alum re­sults for Grand Lake St. Marys look good, ac­cord­ing to a re­searcher. But the suc­cess needs to be quan­ti­fied for state of­fi­cials to de­cide whether to ap­ply more."