There are fables such as this one suggesting that fish do better in a pond whose surface is pierced by one or several obstacles, such as rocks. The rationale is that such "islands" turn the pond into channels, encouraging more movement and therefore well-being of the fish. I wonder - is that true - or just an urban legend?
First of all yes this is an urban legend but it is true that a pond with objects that pokes out of the water can help increase the quality of life for your fish.
Rocks in a pond or in a stream will slow down the waterflow and create a micro environment for plants and other life in the water,this can improve water quality for your fish.
Rocks that pokes out of the water and rocks on the bottom of your pond will provide a larger surface for bacteria to grow on,the rocks will be hiding places for insects and this will provide some snacks for the fish that they have to hunt for to get.
BE SURE TO ONLY USE ROCKS THAT ARE SAFE FOR YOUR POND,do not use marble or rocks containing dissolvable minerals or metals,river rocks and rocks from streams are in general safe to use in your pond.
I remember also that something poking out of the water hinder the surface to freeze completely, and this would give some more oxygene into the water? Apr 15, 2022 at 6:53
2@Allerleirauh putting a ball in the water keeps an area of open water during winter,it is used to let toxic gasses like methane and co2 escape from the water,cold water will be saturated with oxygen so as long as one get the co2 out the fish will be fine. Apr 15, 2022 at 12:01
1A stream is much more effective improving conditions than some rocks. I have a 30 ft/10M stream for my small pond. Flow is about 200 gal/hour with a low wattage pump ( 30 watt ?). Danios jump the few 3" drops to lay eggs. Only problem I now need to get rid of 100+ giant danios and chain pet shop won't take them. The stream also replaces a filter. The referenced article was likely written by a "writer", not someone familiar with ponds. Apr 15, 2022 at 15:24
@blacksmith37 a stream with rocks and plants are better than putting the rocks in the pond but having rocks in the pond will provide a micro climate for insects and other life living off waste in a pond,i focused on the in pond question this time but next time if we get a question about streams i can focus on that :) Apr 16, 2022 at 3:42