Top 3 reasons to use gravel
Biological filtration
All the nooks and crannies provide habitat for microbes to process nutrients, along with areas for plants to grow, which help keep the water clear
Gravel is especially valuable in wetland filters, which are easy to maintain, though they require very little, and blend seamlessly into the landscape with the natural beauty of plants.
Natural Beauty
Ponds with gravel mimic a tumbling mountain stream! They blend seamlessly into the landscape, with the help of big stones.
Liner Protection
Bare liner subjected to the sun degrades faster than those protected with gravel.
Plus the layers of stone give the liner physical protection from everyone who like to swim in the pond!