(Viral Hemorrhagic Septicemia)

By: Chris Hamerla

What is VHS:

VHS is a viral disease known to infected at least twenty-eight species of fish. Originally from Europe, VHS was documented in the State of Washington in the late 1980’s. In 2005 and 2006 large fish kills in Lake Huron, St. Clair, Erie, and Ontario and the St. Lawrence River occurred. These fish kills were diagnosed as VHS and the first time VHS was ever found in the Great Lakes. Lake Michigan waters surrounding Wisconsin and the Lake Winnebago System, within Wisconsin, had fish that tested positive for VHS in 2007. As of January 2010, VHS-positive fish were found near the Paradise/Whitefish Point on the east side of Lake Superior. Since the St. Mary’s River adjoins Superior with Lake Huron, it has been anticipated that VHS would eventually be found in Lake Superior. Paradise/Whitefish Point is just across Whitefish Bay from the mouth of the St. Mary’s River. VHS regulations remain the same with a renewed emphasis on education and prevention steps. VHS is also known in lakes in Michigan (Budd Lake and Baseline Lake) and New York (Conesus Lake, Skaneateles Lake, Seneca-Cayuga Canal, and a private pond).

Exactly how VHS first made its way to the Great Lakes isn’t known. Several ways seem likely. Water in the ballasts of ships might have been contaminated. Migrating birds or fish may have carried the virus.  Frozen herring, used for bait, may have been contaminated. What is know is how VHS spreads.

VHS is spread through the urine and reproductive fluids of fish. Infected water that is introduced to non-infected water can also spread the disease. Fish are most susceptible during colder water periods and when they are physically stressed. VHS is most active in water temperatures from about 37 – 54°F. This combination makes the spawning period, for many fish, a prime time for VHS to infect fish. The range of water temperature is also significant since cooler lakes, like Lake Superior, maintain a climate that is very suitable for VHS. Other stress factors including poor water quality, excessive handling, and lack of food can increase a fish getting VHS. When fish are stressed their immune systems aren’t able to fight off disease as they normally would.  Not all fish that become infected die. Fish that are infected do carry the virus.  VHS can remain infectious for at least fourteen days. Fish that live do build up antibodies against VHS. However, after a period of time the antibodies diminish and the fish is at risk again. VHS can be spread when a fish eats an infected fish. VHS is not a human health concern however precautions should be made when handling any sick looking fish. Symptoms of VHS include internal and external hemorrhaging (bleeding) and bulging eyes.

Why is VHS Harmful:

As mentioned above, VHS can kill fish. When certain year classes of fish are together the possibility of loosing the entire class to VHS  is a concern. VHS is easily spread between fish and water bodies. Since fish in new water bodies aren’t immune to VHS large fish kills occur. The virus targets all ages and numerous species of fish.

How to Control VHS:

There is no treatment for VHS. Controlling it is a matter of preventing infected fish and/or water from getting into a uninfected water body. There will always be the possibility of migrating birds and fish transporting the virus but people can take precautions to prevent the spread.

Traveling from one body of water to the next is a common practice for many boaters and anglers. To prevent the spread of VHS and other invasive species all water needs to be drained from the boat and gear before leaving that water body. This includes water in live wells, bilges, ballast compartments (on ski/wake board boats), and in bait buckets. If minnows are caught from the wild they should only be used on that water. Minnows bought from licenses bait dealers are tested to be free of VHS and are safe to use on multiple water bodies so long as no other fish or lake or river water was added to the container. The concern is that infected bait, water, or fish will contaminate a new water body.  Live fish should never be introduced or released into a body of water unless they are part of a regulated stocking program. In many states, including Wisconsin, this is illegal. Again, these fish could be carrying viruses or diseases that will infect the new area. Newly introduced fish species may also have negative effects on existing populations of plants, animals, fish, and water quality.

Following these precautions is the best way to prevent the spread of VHS. Since its discovery in 2007 the State of Wisconsin has been testing water bodies across the state. To date, other than the Winnebago System and Lakes Michigan and Superior, no water bodies have tested positive for VHS. Testing is done throughout the state including water systems surrounding infected waters.

Again, the best way to prevent spreading VHS is to drain all the water from the boat and equipment before going to another water body. If the boat has been on known VHS water it should be thoroughly washed and/or dried before launching into another water body. Live fish should never be transferred to different waters.


Chris Hamerla is the Aquatic Invasive Species Coordinator of Lumberjack Resource, Conservation, & Development Council serving Lincoln, Langlade, and Forest Counties in northern Wisconsin. As the Aquatic Invasive Species Coordinator, Chris focuses on implementing AIS prevention and control efforts through public awareness and education programs. For more information or have any questions contact Chris at 715-362-3690 e-mail chris_h@frontier.com



Learn more about each Aquatic Invasive Species (AIS) Click on the Links Below:


Eurasian Watermilfoil
Curly-leaf Pondweed
Rusty Crayfish
Asian Carp