Evasive water plant ?
More photos to show the shape of a single leaf, and possibly a flower, will help us identify the plant. Also, is this a managed or landscape pond, or in a wild area?
The local Master Gardener Volunteers will know plants in the area best, so contacting them may be worthwhile: Calaveras County Master Gardeners Hotline: 209-754-2880 - Messages can be left at anytime. A Master Gardener checks it every day. Help Desk: Only Wednesdays - 10:00 am to 12:00 pm: Phone: (209) 754-6473 Email: firstname.lastname@example.org http://ucanr.edu/sites/CalaverasCountyMasterGardeners/About_Us/Contact_Us/