It is ugly, messy even. Sometimes it stains fishing line and leaves boats discolored. It makes fishing tough too. It is algae, the green stuff that appears on the surface of many North Dakota lakes during warm summer days.
This year the first algae blooms may have arrived a few days earlier than expected, but it was an early spring too. Algae changes the appearance of a favorite fishing lake in a few hours time. Blooms are not unusual, but they can be an indicator of trouble brewing on a body of water.
"We just came off historic flooding. Decomposition is more than ever. It is a great recipe for stink," said Greg Power, North Dakota Game and Fish Department fisheries division chief. "In North Dakota we have more winter kills than summer kills, so it is hard to predict."
Algae in bloom on Lake Audubon. Such occurrences are not unusual for North Dakota waters, but can lead to a depletion of dissolved oxygen.
Reservoirs are particularly vulnerable to algae blooms. Algae blooms have been common for years at Lake Darling, including this year, but they seldom lead to fish kills. Duane Anderson, Upper Souris National Wildlife Refuge, has been monitoring the condition of the reservoir.
"There is vegetation. The weeds are growing, typical for this time of year," said Anderson. "Right now we don't consider it critical."
When algae dies, it consumes oxygen. Given the right conditions, such as an extended period of warm temperatures with little water movement, an algae die-off could play a significant role in the health of a lake, river or reservoir.
"It is not the daytime highs, but rather the nighttime lows that really jumps up the water temperature," said Power. "The nutrients are always there, always waiting for warm weather."
The water temperature on Lake Darling rose to over 80 degrees July 7. A few days later, it dipped back into the upper 70s, still considered quite warm for North Dakota water in early July with the historic hot weeks still to come.
"If the water temperature pushes 85 it is lethal for northern pike," stated Power.
Recently a pike kill developed in the James River. The water temperature rose in the shallow river and left pike with no cooler water. When water gets too warm for their liking, pike will seek out deeper, cooler water. If there is none available, pike are in serious trouble.
Power said he doesn't consider this year's algae blooms and water temperatures to be much worse than normal, but adds that at least some summer kills are inevitable. Some lakes are simply too shallow to provide fish with protection from an extended period of high temperatures. Power lists northern pike and trout as being particularly vulnerable.
Summer fish kills can occur in a matter of hours. Fishermen who enjoy excellent fishing one evening could find the same lake depleted of oxygen by the following morning. It takes somewhat of a perfect storm for that to occur, such as a combination of an algae die-off, very warm nighttime temperatures and calm conditions.
"I'm looking forward to somewhere around August 20," said Power. "Inevitably that's about the time we get cool nights, northwest winds and the lakes start turning over."
"Turning over" is a reference to the thermocline, the layer of cool water in deeper lakes that begins to mix with warmer water from above as temperatures moderate. The result is generally improved fishing as deepwater-dwelling fish begin to move back into shallower water. The depth of the thermocline depends on water temperatures.
The last critical year for water temperatures, said Power, was in 1988 when water levels were low and summer temps were high. Game and Fish crews will begin testing for dissolved oxygen in the coming weeks.