Silt and covering rock formations near a spring are separate issues.

Silt -- It's almost never good for a pond. Silt build-up reduces the storage capacity of your reservoir and, if it contains organic material, the resulting layers can be a mucky, stinky mess in the pond bottom. When construction budget and space allow, many pond designers create a small catch basin upstream from their main project, just to collect silt. In some states, you get all sorts of attaboys from the government for creating . . . ta-da . . . wetlands.

Springs -- They're God's gift to us pond owners (read challenge), and must be treated with respect. Most contractors I have worked with choose a site carefully. They build a pond so that, when full, the pond's water level does not reach the elevation of where the spring emerges. That way, you're working WITH nature, not against her.

As for placing a layer of so-called "silt" over a rock layer below the surface of the water, don't expect your handiwork to last. The loose sediment will slough off and seek its own level, usually filling any low spots in the main lake basin.

Hope this helps.

Editor, Mark McDonald