Want to get up close and personal with a plant that looks like this?
It’s an invasive water chestnut (Trapa natans), and Boston’s rivers are full of them!
Water chestnuts clog waterways, making it hard for other plants and fish to survive, and they produce big nasty seeds to boot. (Although one enterprising netizen has observed that from the right angle, they do resemble Dobby the House Elf from Harry Potter.) You can read more about them here.