On Vancouver Island the tides rise and fall up to 3 feet every 12 hours of so. As a consequence, in locations where there is little slope, great expanses of tidal flats appear. In some places, you can walk almost a mile from the high tide level. It is a very interesting experience to walk out onto an enormous flat expanse of sand that is underwater two times a day. I thought these aquatic plants were unusual because they look vaguely like crab claws.