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Invasive Aquatic Plant

This article was written by Bob Bowles for and appears online and in Orillia Today.

New invasive aquatic plant taking over Simcoe County ditches and waterways.

European frogbit grows quickly, says Bob Bowles

Several hours spent monitoring lakes, rivers and creeks in North Simcoe has made me realize roadside ditches, creeks and small streams are being choked out by a new invasive aquatic plant native to Europe.

European frogbit (Hydrocharis morsus-ranae) was unfortunately brought to the Central Experimental Farm in Ottawa in 1932 for possible commercial use as an ornamental plant. In 1939, it was found in the Rideau Canal and has since spread to several rivers, lakes and inland waters.

I first observed it in 2015 in Stony Lake in the Kawartha Lakes region, where it now chokes out some areas. In 2018, I observed it in Canal Lake, east of Brechin.

It was just a matter of time before it reached Lake Simcoe, but I was amazed this August to find large mats choking ditches around Mara Point and creeks like Barnstable Creek, Waiman Creek and Murphy Creek in Ramara Township. It is starting to establish itself in Mill Creek and Broughs Creek in Orillia, Oro-Medonte and Severn.

It has a well-developed root system that normally does not anchor the plant in substrate but rather floats free, sometimes putting down roots 50 centimetres long. It spreads by stem fragments, seeds, winter buds and runners, and is carried by boats, recreation and wildlife.

Plants form a rosette (six centimetres across) and wide leaves the size of a Canadian dollar coin with rounded apex and heart-shaped bases. Leaves are green above and purple-red beneath. Flowers two centimetres wide have three white petals and a yellow centre.

Plants grow quickly into large tangles that deplete oxygen levels, impact fish communities and aquatic wildlife, crowd out other plants, and restrict recreation like boating and swimming. It prefers slow-moving waters like ditches and creeks with mud bottoms. Care must be taken when moving recreational equipment to new areas to prevent the spread of this invasive plant.

By Bob Bowles Orillia Today

Sunday, August 22, 2021

Invasive European Frogbit

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