Noxious Aquatic Weeds and Osoyoos Lake

Canada’s “Least Wanted” List

Aquatic vegetation is an important part of the biology of Osoyoos Lake. However, many non-native plants have been introduced into the lake over the last few years, and have become (or are potentially) extremely invasive.   They grow and spread rapidly, choking out native plants, impeding recreation and competing for oxygen in the water.  Many of the weeds listed are found in aquariums and ornamental water gardens, and this is probably how they get to be introduced into the lake.

How can I help control these weeds?
  •  Learn to identify them.
  •  Make others aware of the danger of these weeds.
  •  Clear all plant material from boats, trailers, anchors, motors etc, then wash with hot water.
  •  Don’t dump unwanted aquarium contents into storm drains, streams or the lake!  Dispose of plants far away from bodies of water.

BRAZILIAN ELODEA: Not yet found in Osoyoos Lake. Originally an aquarium plant, it is related to the Hydrilla.  Resistant to everything known.  Will choke out everything else that grows in water (including milfoil!) Forms a dense green mat.

BLUE-GREEN ALGAE: Not actually a weed, but it is a concern in Osoyoos Lake. Simple one-cell organisms or bacteria, they need light to reproduce and survive.  They thrive in warm, shallow, slow-moving water. A small amount in a lake is healthy: but large amounts, as often occur in hot summer months, block out light and use up oxygen in the water, inhibiting plant growth.  Osoyoos Lake has a large amount of algae due to high nutrient levels in the water.

EURASIAN MILFOIL:  An aquatic weed, prevalent in Osoyoos Lake. Highly invasive.   Has been the #1 problem in Okanagan lakes since 1975. Originally an aquarium plant.  Spread by boats & trailers. Even tiny fragments root easily. Effective methods of control have not been found yet.   

PURPLE LOOSESTRIFE: Spreads quickly along roads, canals, drainage ditches and wetlands. Ornamental plant, originally used by beekeepers.  Tall (up to 7 feet) stems with purple flowers produce up to 2.7 million seeds each.  Invasive and widely established. Seen on Channel Parkway Penticton and other low-lying areas.  Can be mechanically controlled to a certain extent, but is almost impossible to get rid of completely – it just keeps coming back!

U.S. Weeds

Many of the following weeds are a huge problem in Washington State and other parts of the US such as Florida. They are not known to occur in Osoyoos Lake – yet….! They may be found in aquariums, and we must ensure they NEVER enter our water sources.

PARROT FEATHER MILFOIL:  Spread by fragments.  Difficult to control.  Grows 6 inches above water.

FANWORT:  Aquarium plant.  Spread by fragments.  Still being sold.

FRAGRANT WATER LILY:  Aquatic garden plant.  Pink flowers.  Likes shallow water.

YELLOW FLOATING HEART:  Aquatic garden plant.

WATER PRIMROSE:  Aquatic ornamental plant.  Yellow flowers.

GARDEN LOOSESTRIFE: Ornamental.  Yellow flowers.

SWOLLEN BLADDERWORST: Seeds spread by birds.  New plant.  Yellow flowers.


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