GARDEN CITY BEACH — For Chad Creswell and his two fishing partners from Shelby, N.C., the superb flounder fishing off Grand Strand piers the last several days signified a nice surprise for their late-summer vacation.

For Dr. Susan Libes of Coastal Carolina University, the latest flounder frenzy signifies the continuation of a disturbing trend in the near-shore waters of the Atlantic Ocean along the Grand Strand - the summertime occurrence of hypoxia conditions.

In less than six hours of fishing Tuesday morning from The Pier at Garden City, Creswell, along with nephew Jesse Hollifield and brother-in-law Rick Hollifield, used mud minnows to catch over 50 flounder, including five keepers over the 14-inch minimum size limit.

To catch flounder in such large numbers is a very rare occurrence, and indicates the fish are moving closer to shore in search of oxygen.

``You can actually see the flounder coming in (toward the beach) near the surface,’’ said Creswell. ``It’s good for the sport fishermen but I don’t think it’s good for the fishery. If the fish are not going to make it because of the (lack of) oxygen, it’s going to hurt it for the future.’’

Last weekend, a number of marine species were found dead on the beach in Myrtle Beach including flounder, pompano, whiting and stingrays.

A similar event occurred in July, 2004, when pier anglers caught incredible numbers of flounder plus there was a small fish kill near Huntington Beach.

At the same time, Libes and her cohorts from CCU’s Environmental Quality Lab were testing the water at the Apache Pier in Myrtle Beach and discovered the likely cause - hypoxia conditions, or low levels of dissolved oxygen in the water.

In May of 2006, the CCU group and the South Carolina Department of Natural Resources established a data station to monitor water temperature, dissolved oxygen levels and salinity at both the surface and the bottom at Apache Pier.

Similar data stations were unveiled earlier this year at 2nd Ave. Pier, in early April, and at Cherry Grove Pier, in early May. Last Wednesday, Libes stated conditions were right for another hypoxia event and she proved prophetic.

One day later, the data stations showed low levels of dissolved oxygen and fishermen began catching unusual numbers of flounder over the weekend.

Libes, Program Director of the Environmental Quality Lab, says since the water monitoring data stations have been in place, she has been able to determine that hypoxia events are commonplace along the Grand Strand in the summer.

``There is low oxygen every summer - some summers are more intense than others,’’ said Libes Tuesday afternoon. ``In 2009 we had anoxic conditions (lack of oxygen in the water) but no fish kills. Of course, we had the 2004 event and now 2012. When a location begins to experience low dissolved oxygen, the low oxygen (events) increase in frequency and intensity.’’

Libes offered several contributing factors that all came together as likely causes of the latest episode.

• Decent rainfall this spring and summer created stormwater runoff.

• Consistent summertime southwest winds into Long Bay followed by light winds below 10 mph.

• No tropical systems have occurred to stir the water up .

• A recent spring tide(a higher-than-normal high tide that occurs twice a month with the new and full moon).

• Warm water conditions.

``A few days of southwest winds followed by a drop of wind speed below 10 mph, when this happens near a spring tide (occurred Aug. 17) I think these conditions are conducive to trapping water and oxygen –demanding substances near inshore,’’ said Libes. ``We have had a lot of rainfall that has been sweeping material into the coastal waters through storm-water runoff. It’s not clear what the source of the oxygen-demanding substances are but we think organic matter and ammonia are the main ones.

``The native bacteria decomposes these (oxygen-demanding) substances such as organic matter and ammonia and thereby consume oxygen.’’

Libes notes that S.C. DNR and DHEC officials are also looking into the possibility an algal bloom that could be occurring.

``It’s possible the algal bloom is the source of the organic matter,’’ said Libes. ``First you have an algal bloom and then the oxygen drops.’’

Libes praised the cities of Myrtle Beach and North Myrtle Beach along with Horry County for helping fund the data stations.

``It’s a real testament to these municipalities to be proactive in recognizing this potential problem and agreeing to collaborate on getting more data,’’ said Libes.

Libes stressed more research is needed to determine the scope of the hypoxia problem. The pier data stations are very helpful but don’t determine how far out into the ocean the hypoxia is occurring.

``We don’t know how far the low oxygen goes offshore or how low the oxygen level is,’’ Libes said. ``I think we really need to moor some continuing measuring devices offshore. The piers are great but we’re only seeing the edge of what is going on.’’