Submitted by Thad Yorks, professor

Cazenovia College

Another invasive aquatic plant species, European frog-bit (EFB; scientific name: Hydrocharis morsus-ranae), is established and threatens recreation around Caz Lake. EFB was first detected at the north end of the lake in 2014 during the annual aquatic plant survey by Racine–Johnson Aquatic Ecologists. It may have arrived by illegal dumping or transportation by waterfowl. Currently, EFB is abundant in the northwest bay and decreases in density to the south along either side of the lake as far as McNitt State Park. If left unchecked, EFB could spread and affect recreation around much of the perimeter of the lake.

As its common name would imply, EFB is native to Europe but also occurs in parts of Asia and Africa. The species entered North America in the early 1930s when it was brought to an experimental farm in Ottawa, Ontario for study as a potential ornamental plant. The plant soon escaped into nearby Rideau Canal and has been spreading ever since. Currently, it is in at least ten counties in New York State.

EFB is a truly floating plant – though its dense roots may exceed 12 inches, these roots generally usually just hang down into the water. Only in very shallow water along the shoreline can the roots actually grow into the lake’s bottom. Being a free-floating plant, it is usually encountered in relatively shallow, sheltered areas and sometimes along wind-blown shorelines.

Its flowers are less than an inch wide, but they are easy to spot slightly above the water’s surface with three bright white petals and yellow centers. The round to heart-shaped leaves look like miniaturized water lily leaves but are easily distinguished from all water lily species by their small size – only 1 to 2 inches wide. The leaves grow in rosettes – clusters of several leaves attached closely together at their base.

If you look at the base of a rosette, you’ll see that they are growing along a horizontal stem called a stolon. Relatively late in the growing season, overwintering buds called turions are formed on the ends of underwater stem-like structures. The turions eventually break off and sink to the bottom until the following spring when they float up and sprout into that year’s plants.

The impacts of EFB are what you would expect from a floating plant that can form dense mats over large areas. These mats make paddling a canoe or kayak very difficult, and you can forget about swimming or running a motorized boat. Even waterfowl find it difficult to use areas of dense EFB. Down in the water column, dissolved oxygen levels are reduced because photosynthesis is concentrated at the surface, and oxygen in the air is prevented from diffusing into the water. Also, the tangle of stolons and hanging roots can actually inhibit the movement of larger fish.

Control and hopefully eradication of EFB can be accomplished by simply hand-pulling and discarding the plants before they produce the next year’s turions. With help from a grant from the NYSDEC, the Town of Cazenovia hopes to eradicate EFB from our lake in the next three years. To aid in the removal we are looking for volunteers to help hand pull EFB plants during August and September.

If you have a kayak or canoe and would like to help, please contact either Thad Yorks at [email protected] or Lauren Lines at [email protected].