Invasive Species

Invasive Species Guide 

Link:  Lake_Simcoe_Invasive_Species_Guide_2021 (3)


See the above authoritative guide for the most up to date information.  The Lake Simcoe, Lake Scugog area lakes have many invasive species, and there are more out there in lakes and rivers that are close to us.  It is essential that we follow the best instructions for how to prevent new invasions:  CLEAN, DRAIN, DRY YOUR BOAT.  Thank you to the Ontario Federation of Anglers and Hunters and the Lake Simcoe Conservation Authority for compiling this guide. 



A brief history of Lake Scugog’s introduced and invasive species

The first major ecological engineer, common carp, was introduced from a dike collapse at a fish farm raising COMMON CARP  for food. They love the shallow, mud bottom and proliferation of aquatic vegetation and often grow to 3 ft or more.  (see photo at left)  These fish are now present is very large numbers, ‘vacuuming’ up the shoreline edges. Although they are herbivores, they are also very good at vacuuming up the newly lain eggs of other fish, especially walleye.

New species WALLEYE were stocked in the lake in the early 1900’s for sport fishing and were very much appreciated until their numbers begun declining about 25 years ago because of habitat loss, the proliferation of bass and BLACK CRAPPIE, over-fishing and the siltation of spawning beds. But the introduction of walleye almost decimated the native mudcats which had previously been numerous and enjoyed by many.

The 1960’s on Lake Scugog saw many motor boats and other water craft arrive trailered in from around  other Lakes and streams in Ontario. They came to enjoy the storied excellent walleye and bass fishery. With these boats, trailers and equipment also brought many invasive plant species, the worst of which was EURASIAN WATER MILFOIL (see photo at right). It was ideally suited to the lake and its high phosphorus and nitrogen levels and quickly out completed many of the native species of the lake.  This species is still the species most disliked by shoreline owners and recreationists.

Then came ZEBRA MUSSELS and QUAGGA MUSSELS which all but eliminated all the native mussel types. These species were kept somewhat in check because of the muddy bottom of the lake since they are filter feeders.

Then came the real problem.  In 2015, the Stewards noticed thick growth of mats of fishing line type green material.  It was identified as a new invasive macroalga, STARRY STONEWORT.  Since that time we have focused most of our research on the effects of the proliferation of this fast growing alga and its very great effects on lakes where it is found throughout southern Ontario.  To find out more about starry stonewort and our research see: