The answer to this question can be a tough one as the growth of any plant can vary due to several factors. One major factor of the growth pattern of aquatic weeds and algae is the location of the NSP or pond. Weed growth, whether it be terrestrial or aquatic, in a warmer climate such as Florida or southern California will be vastly different from weed growth in a cold northern climate such as Maine.
In general, however, you can expect to see different pond weeds pop up at different times of the year based on environmental temperature, just like the dandelions and clovers in your lawn will grow and flower at different times during the spring and summer. If your NSP or pond freezes over, the perennial weeds will typically die back in the winter and re-emerge in the spring. Some plants, however, will continue to grow throughout the cold season, though at a much slower rate than you’d see in the warmer summer months.
Trouble surfaces when water temperatures drop to the point where algaecides and herbicides become ineffective, but the weeds continue to grow. Algaecides such as copper, for example, stop working when the water is below 60° Fahrenheit. In addition, beneficial bacteria in an aquatic environment slow down and will even become dormant when temperatures fall below 50°F.
It should also be noted that some winter algae blooms can be beneficial once spring arrives. Diatoms, a major group of algae, can thrive in the winter as they take advantage of reduced competition from other plants that grow through the summer. Come spring this will benefit the NSP as diatoms with take out nutrients in the water, and other beneficial organisms will in turn eat the diatoms leading to clear water.
Unfortunately, if you are seeing an excess of algae growth during the winter months and the water temperatures are below 60° Fahrenheit, there is not much you can do to fight it, other than manually removing it, until temperatures rise in the spring and beneficial bacteria begins to thrive again. Just know that this a normal part of an aquatic environments life cycle.