The abundant spring and summer rains helped both Georgia sport fish and anglers this year. Higher lake levels meant good spawning habitat for bass and plenty of water covering the ends of boat ramps. Overall, higher reservoir levels are beneficial to sport fisheries, according to biologists with the Georgia Department of Natural Resources, Wildlife Resources Division (WRD).
But, they say there is one down side to the abundant rains of 2005: higher runoff from the land washes even more tree leaves, lawn clippings and fertilizers, carrying nitrogen and phosphorus nutrients into those streams. The streams take the nutrients that are food for microscopic plants and animals (phyto- and zooplankton), downstream to the reservoirs, where they fuel the growth of plankton. Plankton consume dissolved oxygen both when alive, and after death when they settle out, and decompose, and use up dissolved oxygen in this process. This is a natural occurrence and as a result many reservoirs have low dissolved oxygen levels near the lake bottom each summer. However, during years of high river flows the deepwater dissolved oxygen problem can become is worse because of the extra nutrient loads that fuel higher lake productivity are decomposing.
Most reservoir fish like largemouth bass, hybrid striped bass, shad and sunfish can tolerate warm water temperatures near the surface of the lake, where dissolved oxygen levels remain high, due to aquatic plant activity called photosynthesis. However, coolwater fish species like walleye and striped bass larger than 10 pounds require cold, oxygenated water to survive and grow. Each summer, the warm water of the lake's top layer forces them down, while the oxygen-poor bottom layer pushes them up. The coolwater fish are "squeezed" into a middle layer of lake water where the temperature is low and the dissolved oxygen is high. In most years and especially in drought years, this middle layer of water is thick and the coolwater fish survive the summer rather well.
This year in many north Georgia reservoirs, that band of cold, oxygenated water is very thin because of the oxygen depletion from additional nutrients. As a result, coolwater fish are stressed this summer in many north Georgia reservoirs like lakes Lanier, Hartwell, Allatoona, and Carters. WRD fisheries biologists are monitoring dissolved oxygen levels and report that coolwater habitat is very limited in those lakes. Mountain lakes such as Nottely and Chatuge have slightly better oxygen levels because of less total runoff and cooler overall weather in the higher elevations. With 4-6 weeks left before cooling nights can begin to lower temperatures on these reservoirs, this situation likely will get more severe, creating greater potential for some coolwater fish to die from angling stress or simply from a lack of oxygen.
WRD fisheries biologists expect most of the fish populations in north Georgia reservoirs to be unaffected by these natural water quality changes. Many coolwater fish are able to find summer refuges in underwater springs or in cooler rivers and streams flowing into the lakes. There should be plenty of sport fish available for anglers this fall and in the coming years. By giving notice of this potential for some fish kills, WRD hopes to help anglers understand the natural stresses on fish populations and not conclude that other water quality problems exist in these reservoirs.
For more information, contact the WRD Fisheries Management Office in Gainesville at 770-535-5498. Anglers can report fish kills by calling the State Operations Center's 24-hour hotline at 800-241-4113. Officials say it is important to report the species, size, rough number of fish, and exact location of the fish kill so that an operator can relay that information to the biologist on call.