Contact the co-op and have them use the spreader truck to put ag lime in the lake. You will get some benefit from liming the pasture but no where as much as by using the above method. Hydrated lime does not last long. It will dissipate in about a mth. Most land fertilizer is not the right mix for water. Example 13-13-13 is a common land fertilizer while 0-46-0 or 8-52-10 are common water varieties.