Several fish kills along the Louisiana have been reported in the past week or so, and a state fisheries biologist said the culprit was low dissolved oxygen levels.

"It's just this time of the year: We get a lot of hypoxic water," Louisiana Department of Wildlife and Fisheries' Joey Shepard told "We need to get some cold weather and start cooling things down."

The largest of the kills was in Plaquemines Parish, and apparently included a lot of pogies and menhaden. However, Shepard said the specific area in question was "pretty much closed off" to fresh water, which aggravated the situation.

There also was a second Plaquemines Parish kill that involved some redfish, but Shepard said that incident was much smaller in scope. Another kill in the upper Barataria Basin was even smaller.

Even though some of these waters were open to larger bays, Shepard said oxygen levels are low in much of the Gulf of Mexico – and that has apparently combined with the recent fronts to cause problems.

 "There's a lot of hypoxic (low-oxygen) water offshore, toward the bottom (of the water column," Shepard said. "It looks like what happened in some of these instances is that, with the little bit of north winds we've had lately, the wind blowing on the surface pushes the surface water offshore and we get some upwelling (of the oxygen-deprived water)."

He pointed out that the offshore hypoxia has not been tied to the BP Deepwater Horizon oil spill earlier this year.

"I guess it's possible because of the bacteria that apparently eats the oil … but (hypoxia) is a natural occurrence," Shepard said. "We get it every year."