They may be.
We have a small network of drains on our local marsh.
The invertabrate life is abundant, so too is the vast aray of plant life.
Sticklebacks are thriveing, so too is the bird life.
Some of the drains are connected to main water coarses or are flooded.
Whats to say a bird with some weed attached lands in the water, that bit of weed may contain a fish egg or two, maybe more.
Or a local river/stream or lake may flood, releasing fish into the drain.
Eels migrate over land to find water.
We often take no notice of small puddles of water or these drains or dithches.but unless we investigate, we will never know what suprises they may hold.
The local motorway has drainage ditches and holding pools for rainwater runoff. I went down there to explor with a few bits of tackle,maggots and bread.
Spent all afternoon catching rudd and tench, went back the following weekend and had much the same including 3 carp to 5lbs.