I have an outside 30 gallon pond that looked similar to this
about 3 weeks ago. now there is not even the water mint left only a few floating pine needles and 2 or 3 snippets of plants less than 1/2 inch long. The only living creatures in it are a large apple snail, about 2 inches in dia, and a crawfish. Both of which had been in the pond for weeks prior to the plants disappearing. The pond is insdide a fenced in area of our fenced in yard and is above grond so only animals that can jump at least a foot can get to it. Any ideas on what could cause this. I was planning on putting in a larger water pond but if this could happen again I don't think I will risk it. On a postive note my ponds inside my greenhouse are fine.