Casca :

Yes I have seen this before. If your water is fertile from last year and you did not have to much runoff during winter when temps get right the bloom will start without fertilizer. In some parts this happens every year without any fertilizer. As Meadowlark often reminds us , that is why you have to be careful in starting a fertilization program . They can get out of control and cause problems.As long as you have visability of 18 inches you should be ok. You should keep an eye on it and not add to the problem . ewest