Aquatic Vegetation

Why are there so many weeds in the lake?

A common question heard around Green Lake some summers is “What is the cause of all the ‘weeds’?” After speaking to several water resource professionals, we found that this question is complex and not specific to Green Lake. Excess aquatic vegetation is an episodic occurence and when it does occur it can make boating, fishing, and other recreational activities difficult for many Wisconsinites.

During the summer of 2010, many lakes in Wisconsin experienced and increase in aquatic vegetation growth. While there wasn't a quick or easy answer, there was a general consensus among water resource professionals that the increase in aquatic vegetation could have resulted from a variety of occurrences:

• Early and very warm springs boost the development of new plants.
• This spring and summer we experienced almost record breaking, above average growing degree days.
• More frequent and intense rain events increase nutrient loads to Green Lake and contribute to increased vegetation growth.
• Periods of calm winds, hot weather and an ample supply of nutrients throughout the summer can fuel the growth of algae and duckweeds.
• According to water resource professionals, the zebra mussel population may be lower in Green Lake when compared to other Wisconsin lakes; however, their presence may contribute to the increased vegetation problem. Zebra mussels in large numbers have the ability to make the water clearer because an adult zebra mussel can filter a liter of water per day, siphoning out all the small particles they encounter. Increased water clarity allows for more light penetration which aids the growth of aquatic plants.

In sum, clear water, nutrients, periods of calm weather, low currents, warm water and other factors could all conceivably affect vegetation growth in Green Lake.