Bonnet Carré Spillway 2016 Opening



1/26/2016 Photo: 1/29/2016 Photo:



The Pontchartrain Conservancy (lpbf) is concerned about environmental impacts of opening the Bonnet Carré Spillway. Past Spillway openings have shown varied impacts on Lake Pontchartrain from increased turbidity and nutrients leading to algae blooms to species relocation. To monitor the impacts that this unprecedented early opening of the Bonnet Carré Spillway will have on the water quality and ecosystem of Lake Pontchartrain, lpbf will begin water quality monitoring on Tues, Jan 12th. We will continue our monitoring activities for a period of at least three months to assess the impacts of the Mississippi River water moving through Lake Pontchartrain. This monitoring will be performed in addition to all of the ongoing monitoring and projects that we have.

lpbf will be performing two water quality monitoring activities:

1) Weekly we will monitor Lake Pontchartrain at Causeway Crossovers 2, 4, and 6 for water temperature, dissolved, oxygen, specific conductance, salinity, pH, turbidity, and Secchi Disk clarity.
2) Twice a month for three months we will monitor ten sites in Lake Pontchartrain running an East-West transect by boat. We will monitor for the parameters above as well as collect samples for Nitrate-Nitrite, Total Nitrogen, and Total Phosphorus for analysis at Southeastern Louisiana University’s LELAP-Accredited Microbiology lab.

The data collected from these two activities as well as data collected by other state and federal agencies, universities, and researchers will be posted bi-weekly on lpbf’s Hydrocoast Maps, making it available to the public via the lpbf website. Our Hydrocoast Maps can be viewed here. lpbf’s water quality data can also be viewed weekly here. In addition, lpbf will update the public through our “Basin Bulletin” e-newsletter, our Facebook and Twitter pages, and our website

Sites are illustrated on the map (1-10 from west to east) (CC-Causeway sample sites from north to south)
***Salinity and Dissolved Oxygen are sampled at the top and bottom of the water column to ensure that hypoxia in not developing with the input of fresh water.

***Bonnet Carre Spillway discharge in cubic feet per second since opening. 

Bonnet Carré 2011

On June 20th, the Corps of Engineers completed the closure of the Bonnet Carré Spillway. On May 9, 2011, the Corps began opening the spillway to relieve flood waters on the Mississippi River. This river water quickly spread across Lake Pontchartrain. Below is the latest update that shows the river water in Lake Pontchartrain.

128 Days After Spillway Opened on May 9, 2011

The image below is the most recent available based on visibility.


Monitoring Lake Pontchartrain after the Bonnet Carré event for algae blooms:

  • From past openings of the Bonnet Carré Spillway, it was anticipated that the excess nutirents from the river water would lead to an algae bloom in Lake Pontchartrain. Water monitoring performed by Dr. Gene Turner of LSU provides a way to know when the algae will be coming. Chlorophyll A is the chemical that makes algae green (and makes photosynthesis happen), and as such is a good indicator of the amount of algae in Lake Pontchartrain. Dr. Turner has measured Chlorophyll A in the lake for years. As the first chart (see below) shows, the Chlorophyll A is usually pretty low and has only spiked in the recent openings of the Bonnet Carré Spillway. The spikes from 1997, 2008, and now are clearly visible on the chart. The second chart also shows how high our current Chlorophyll A levels are (green circles) as compared to years without a river diversion (black circles). The chart also shows that the chlorophyll A levels were very low at the beginning of the year until the spillway opened (green circles) so we know that the rise in Chlorophyll A levels is from the spillway opening. These high Chlorophyll A levels tell us that the conditions were right for an algae bloom to occurr soon.
  • While it appeared that an algae bloom was beginning to form at the end of August (right on time), it seems as though the passage of Tropical Storm Lee may have changed conditions in Lake Pontchartrain enough to end the bloom.  During the storm, southeast Louisiana experienced a lot of rain and wind, adding water to the lake and churning it up.  The storm surge also pushed salty gulf water into the lake.  Whereas salinities in the lake were at about 1 to 1.5 parts per thousand (very fresh) before Lee, they are now between 2 and 5 ppt (nearly normal for the Lake at this time of year).  The actions of the rain, wind, and storm surge seem to have dissipated any blooms that were forming. Since the algae can not grow in salty water, the increased salinities (and now cooler weather) mean that we are unlikely to see a bloom at this point. Nature may have helped Lake Pontchartrain avoid an algae bloom this time. It is important to note that after an opening of the Bonnet Carré Spillway it is still extremely likely that an algae bloom will occur in the lake.  lpbf will continue to work with federal and state agencies in the optimum usage of the Bonnet Carre, including diverting small amounts of Mississippi River into the adjacent wetlands to nourish and freshen them.
  • From past Bonnet Carré openings, we anticipate that the Lake will be returning to normal conditions in about 6 months.


Recreation in Lake Pontchartrain as a result of the Bonnet Carré Spillway Opening: 

  • From analyzing past Spillway openings, we anticipate that much of the negative impacts will be over by the end of the year. So, for the duration of this event, the lpbf advises caution when recreating in Basin waters that you believe may be mixed with Mississippi River water. Boating and other non or limited contact activities should still be fine.
  • Because the lake conditions are expected to change, you should monitor lpbf and agencies for advisories regarding recreation on Lake Pontchartrain. Please check lpbf weekly water quality results online or in the Times Picayune.

Impacts of the 2008 Bonnet Carré Spillway opening:

lpbf used its Water Quality Monitoring Program to monitor Lake Pontchartrain’s water during the 2008 Bonnet Carré Spillway opening. The objectives were to distribute information to the public, identify pollution sources, and provide research data. Click here to read the full report.