By ROBIN SHANNON

L’Observateur

LAPLACE – Water from the Mississippi River pouring into Lake Pontchartrain through the Bonnet Carre Spillway will not drastically affect the height of the lake but could wreak havoc on some of the fragile ecosystems living within the lake waters.

Coastal scientist John Lopez, Ph.D., the acting executive director of the Lake Pontchartrain Basin Foundation, said water heights near the mouth of the spillway may rise briefly, but they will quickly drop off as water gets displaced. He said the lake’s high surface area, coupled with water lost through the Rigolets cancels out any gain from the spillway.

“Lake water rises for different reasons,” Lopez said. “Tides and strong winds could kick up waves that could be slightly increased by the river water but not enough to be significant.”

Lopez said the fresh water pouring into the lake will, however, change the color of the lake to what he described as a “pea soup” green as more nutrient-rich water mixes with the brackish salt water of the lake. The new influx of water will also cause various fish species more accustomed to lake water to migrate to where the salinity content is higher.

Lopez said speckled trout, redfish and other finfish will be pushed out into the marshes on the north and south shore, or further east, while freshwater species like catfish, carp and bass take over.

Lopez also said brown shrimp and blue crabs will also make an exodus out of Lake Pontchartrain as the fresh water continues to pour in. He said fisherman will have to go further out past the Rigolets and into Lake Borgne to get crabs and shrimp normally pulled from the lake.

A bigger concern for the lake is the timing of the opening of the spillway. Lopez explained that this is the latest the flood control system has opened, meaning the heat of summer will play a part in how the fresh water reacts with the environment.

“As freshwater nutrients enter the lake, it’s more than likely that algae blooms will form, and they could be widespread,” Lopez said. “There is very little circulation along some of the shorelines and in harbors, and this will deplete the oxygen in those areas causing fish kills.”

Using information from when the last time the entire spillway was opened, back in 1997, Lopez said fish kills and algae blooms could last for at least a month after the spillway is closed.

Lopez advised that anytime an algae bloom is seen, it is important to avoid swimming or jet skiing in and around it. He said some of the algae produce a neuro-toxin that can affect a person’s nervous system depending on the amount produced.

The good news out of all of this is most of the effects will only be short term. Lopez said the lake is in the best shape it has ever been in, and it has the ability to heal itself over time. He said eventually, the nutrient rich water will cycle out and the saltier water will return.

“It could take anywhere from six to eight months for the lake to return to its normal state,” Lopez said.