Corps fisheries biologist gives the facts on striped bass mortality event at Hartwell Lake

By Jamie Sykes, USACE Savannah District Fisheries Biologist

You may have read reports in the media about a recent fish mortality event at Hartwell Lake. As the fisheries biologist for the U.S. Army Corps of Engineers Savannah District, I’d like to provide some facts on this situation and tell you what we are doing about it.

On the weekend of Sept. 7, we received reports of striped bass floating on the surface in the lower portion of Hartwell Lake, from the dam upstream approximately 2.5 miles. We investigated the event immediately in coordination with the South Carolina and Georgia Departments of Natural Resources (DNRs). We will continue to monitor water quality and habitat conditions until we have cooler water temperatures in the late fall.

This mortality event had been a concern for several weeks. Striped bass habitat conditions in the lower portion of Hartwell Lake have been declining for the last two months with very little striped bass habitat available, which contains both cool water and adequate dissolved oxygen.

Due to exceptionally high rainfall at Hartwell this summer, we have released high outflows from the Hartwell Dam over the last few months. These high release rates were necessary to manage the flood conservation pool and reduce flood risk.

These sustained high outflows affected the temperature and dissolved oxygen levels in the lake, which in turn impacted striped bass habitat. Striped bass prefer cool and oxygenated water that is generally found from 40 to 80 feet deep in Hartwell Lake during the summer months. The high amount of rainfall and inflows that we experienced this spring and summer resulted in much of the water at this 40 to 80 foot level being released through high generation outflows. The cool water that was released through the dam was replaced by warmer water with lower oxygen levels, which impacted Striped bass habitat in the lower portion of Hartwell Lake.

Some anglers have suggested that spilling the water through the spillway gates would have been a better option for moving the large amount of water that has been generated through the Hartwell Dam. This perhaps would have prevented the release of some portion of the cool water from Hartwell Lake, but this option would have also seriously impacted the trout fishery in the Hartwell tailwaters and the trophy striped bass fishery in the upper portion of Richard B. Russell Lake. Both of these fisheries rely on the cool water being released through the Hartwell Dam. Releases through the spillway gates are from the surface of the Hartwell Lake and would be in excess of 80 degrees Fahrenheit in temperature. This water is much too warm for rainbow trout or striped bass.

Summer striped bass mortality events are common in other Southeastern reservoirs, particularly lakes such as Greenwood and Murray in South Carolina, and Lake Norman in North Carolina. However, this is the first summer mortality event that has occurred in Hartwell Lake in the 30+ years that Striped bass have been stocked. The weather conditions that led to this are very unusual. It is also important to remember that the water quality in Hartwell is generally very good and remains safe for fishing, boating, swimming, etc.

 

About US Army Corps of Engineers Savannah District

The U.S. Army Corps of Engineers Savannah District oversees a multi-million dollar military construction program at 11 Army and Air Force installations in Georgia and North Carolina. We also manage water resources across the Coastal Georgia region, including maintenance dredging of the Savannah and Brunswick harbors; operation of three hydroelectric dams and reservoirs along the upper Savannah River; and administration of an extensive stream and wetland permitting and mitigation program within the state of Georgia. Follow us on Twitter @SavannahCorps and on Facebook.com/SavannahCorps
This entry was posted in Fish and Wildlife, Water Management and tagged , , , , , , , , , , , . Bookmark the permalink.
  • jd

    What percentage of the Striper population in Hartwell were affected by this “mortality event”? Is anything being done to replenish for fall fishing on the lake?

    • We are not certain of the exact number of fish, though the Corps of Engineers biologists did make an estimate of approximately 500 fish that were observed during the event. Both SC and GA DNRs continue to monitor the event and they will determine if any changes in future stocking rates will be required to compensate for the mortality. ~Jamie

      • jd

        How many fish make up the average total Striper population in Hartwell?

  • MB

    So the trout in the tailwaters and the stripers in Russell are more important that the stripers in Hartwell? Hartwell gets the short end of the stick again!

  • This update was just provided to us from South Carolina Department of Natural Resources (DNR): Georgia DNR and South Carolina DNR collectively target stocking seven striped bass per acre and 8 hybrid bass per acre per year in Lake Hartwell. Both agencies work together to monitor survival of stocked fish using a fall-winter netting protocol. Agencies have also worked together in conducting late-winter electro-fishing of striped bass to monitor population dynamics such as relative abundance, length and age distributions, relative condition of fish and other indices of the population. Both agencies will consider the potential impact of this summer’s mortality, along with evaluations of the striped bass population conducted this fall and winter, and make a decision on the targeted stocking rate for 2014 and perhaps beyond. Another factor which may play a factor in targeted stocking rates is the fact that Lake Hartwell refilled this year after a period of sustained drought. This typically means primary productivity and forage populations for striped bass increased, and will be considered when planning future stocking rates.

  • JPL

    We are still waiting for an answer on the question submitted….What is the typical population of striped bass in Hartwell, and if indeed about 500 were killed, what percentage of the overall population does that represent? What is the estimated current Striped bass population in the lake at this time?

    Also in regards to the comment that releasing the warm water over the dam would have damaged the river trout and Russell striper populations, why then was it OK to release the high volume of water thru the gates earlier this year? The water at that time was approaching 80 degrees. You can’t have it both ways..JPL

    • JPL: the answer to your first question can be found in the comment we submitted below from SCDNR. Both states target a stocking rate of seven striped bass per acre per year in Lake Hartwell. Given the surface acreage of the reservoir, that comes out to nearly 400,000 striped bass per year. Concerning the current striped bass population at this time, we do not know the answer.

      Your second question: “… why then was it OK to release the high volume of water thru the gates earlier this year?” The answer is in the intense volume of rainfall we received in the first week of July – more than 600 percent of normal – on top of the reservoir level already being above full at the time. Releasing from the spillway was a necessity to prevent floodwater from overtopping the dam, which would have been a significant safety concern – perhaps even resulting in catastrophic damages. We avoid releasing water through the spillway unless completely necessary because it amounts to wasting clean energy. Whenever we release water, we do it in the most efficient way possible, and that involves passing it through the generators. This is one of the main purposes of the dam.

      I hope this answers your questions.

      Best,
      Russell

  • JPL

    What is the latest update to the striper kill? I have been out trying to find fish in my normal spots for this time of year and I am locating nothing.
    Please provide the public with an accurate estimation of the damage done.

    • There’s no new information to report at this time, but we are no longer seeing striped bass rising to the surface of the lake. Please refer to the details in the comment threads below as far as estimated fish affected and the stocking population. Thanks for reading. ~Tracy R.