A natural phenomenon

By Jim Beasley

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An unfortunate occurrence this time of year is the phenomenon known as “fish kills,” where large numbers of dead fish appear on the surface of lakes and ponds, or wash up on beaches. At first sight, it would appear to be the result of something sinister. A closer look usually reveals its origin to be purely natural.

Here in South Carolina, we have many types of fish living in our waters. They flourish in neighborhood ponds and streams, and coastal anglers enjoy the fish that commune in harbors and near jetties. Some of those fish are hardier than others, capable of withstanding the conditions that can produce stress.

All bodies of water contain dissolved oxygen, a measurable level of oxygen contained in the water. Fish and other organisms in the water rely on this dissolved oxygen in order to survive.

Cool water can hold more oxygen than warm water, with variations resulting from seasonal conditions or the time of day or night. When temperatures climb throughout the summer months, and stream flow is reduced, the water temperatures rises and produces a situation known as “hypoxia” or low-dissolved oxygen.

If the oxygen levels drop below a critical level, the stress that is placed on the fish can become too much for them, resulting in a die-off that litters the water’s surface or beaches with (potentially smelly) fish carcasses.

Although most fish kills in summer months are naturally-occurring, some can be the result of human error or other man-made conditions. If you observe a fish kills that should be investigated, contact DHEC’s toll-free emergency response line at 1-888-481-0125.

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