Slough Ice

Yesterday three of us went for a socially distant walk in Central Park in Roseville. We were on the board walks over the slough. We could hear and see red winged blackbirds calling. A red shouldered hawk called from above. We came upon this artistic piece of slough ice. Look at the patterns in the ice! I see butterfly wings and tulips and peonies and maple leaves and a dragonfly and a wood nymph. What caused these lines in the ice? Did creatures underneath or plant materials soaking up the sun and radiating heat create this?