The mystery of the water feature

Generally speaking, I wander down each morning to my water feature to feed the fish, and it looks something like this.

Many mornings, I get to see several blooms like these.

Yesterday morning I wandered down and was greeted by this.

Now, you may recall, that last weekend I cleaned out the pot and replaced the water, so it would be nice and fresh for the fish while I was away. At the time I noticed there were a number of leaves that had been very neatly severed about six inches down the stem.

I was really puzzled. The fish have never damaged the water lily, which provides them with protection from the sun and predators. Each day last week, there were more and more free-floating leaves that had been detached from the plant.

Yesterday morning, it was ridiculous. There were virtually no leaves left, so I investigated. Of the few remaining leaves, several were damaged.

I swished my hand through the water to retrieve all the fragments and saw a flash of orange, way too small to be one of the goldfish.  This is what I caught...

 A tiny little prawn or shrimp...

I couldn't risk losing the last couple of leaves, so the critter was summarily dispatched. But my very kind-hearted brother visited yesterday and questioned whether I had acted hastily. So now the self-recrimination and the questions begin... 

Has anyone ever had this problem? Do you think the crustacean was the culprit or the victim of a miscarriage of justice? How could anything do this much damage in a week? And how did he get there? It's only a small pot, so I doubt he could have arrived on the legs of a water bird like in a big pond or a lake. It is a mystery to me.