Water Crowfoot (Ranunculus spp) aka Water Buttercup
Water crowfoot is a submerged plant that grows in water depths up to 6 feet. The leaves occur on long, branching stems emerging from trailing runners or buried rhizomes. Leaves can be branching, dissected, and fan-like, or lobed, and are arranged alternately along the stem. It produces small yellow or white buttercup-like flowers with five petals.
Leaves of water crowfoot appear similar to fanwort, but do not have the stems associated with each “fan,” and the leaves are not directly opposite. Water crowfoot may also resemble water marigold, but it does not have the upper emergent leaves. Both water marigold and water crowfoot have yellow flowers, but the flower of water marigold is more robust. (Excerpted from Aquatic Plants and Algae of New Hampshire’s Lakes and Ponds, and Maine Field Guide to Invasive Aquatic Plants)