Water fern is a common name for several plants and may refer to:

• Salviniales, an order of aquatic ferns
• Austroblechnum lanceolatum, syn. Blechnum chambersii, lance water fern
• Austroblechnum patersonii, syn. Blechnum patersonii, or strap water fern
• Austroblechnum penna-marina, syn. Blechnum penna-marina, or alpine water fern
• Azolla filiculoides
• Bolbitis heudelotii, or African water fern
• Cranfillia fluviatilis, syn. Blechnum fluviatile, or ray water fern
• Histiopteris incisa
• Lomaria nuda, syn. Blechnum nudum, or fishbone water fern
• Oceaniopteris cartilaginea, syn. Blechnum cartilagineum, or soft water fern
• Osmunda regalis
• Parablechnum wattsii, syn. Blechnum wattsii, or hard water fern
• Regnellidium diphyllum, or two-leaf water fern
• Salvinia molesta, or giant water fern
• Telmatoblechnum indicum, syn. Blechnum indicum, or swamp water fern