Louisiana's earliest and most pressing environmental problem was the chronic danger of flooding by the Mississippi River. In April and May 1927, the worst flood in the state's history inundated more than 1,300,000 acres (526,000 hectares) of agricultural land, left 300,000 people homeless, and would have swept away much of New Orleans had levees below the city not been dynamited. The following year, the US Congress funded construction of a system of floodways and spillways to divert water from the Mississippi when necessary. These flood control measures and dredging for oil and gas exploration created another environmental problem—the slowing of the natural flow of silt into the wetlands. As a result, salt water from the Gulf of Mexico has seeped into the wetlands.
In 1984, Louisiana consolidated much of its environmental protection efforts into a new state agency—The Department of Environmental Quality (DEQ). Among its responsibilities are maintenance of air and water quality, solid-waste management, hazardous waste disposal, and control of radioactive materials. According to the Louisiana Environmental Action Plan (LEAP to 2000 Project), toxic air pollution, industrial and municipal wastewater discharges, and coastal wetland loss head the list of state residents' environmental concerns. Louisiana's problem in protecting its wetlands differs from that of most other states in that its wetlands are more than wildlife refuges—they are central to the state's agriculture and fishing industries. Assessment of the environmental impact of various industries on the wetlands has been conducted under the Coastal Zone Management Plan of the Department of Natural Resources.
The two largest wildlife refuges in the state are the Rockefeller Wildlife Refuge, comprising 84,000 acres (34,000 hectares) in Cameron and Vermilion parishes, and the Marsh Island Refuge, 82,000 acres (33,000 hectares) of marshland in Iberia Parish. Both are managed by the Department of Wildlife and Fisheries. Louisiana's coastal marshes represent almost 40% of such lands in the country.
With approximately 100 major chemical and petrochemical manufacturing and refining facilities located in Louisiana, many DEQ programs deal with the regulation of hazardous waste generation, management and disposal, and chemical releases to the air and water. Trends in air monitoring have, for example, continued to show decreases in criteria pollutants. In 1993, Louisiana became one of the first states in the nation to receive federal approval for stringent new solid waste landfill regulations, and the department has developed a Statewide Solid Waste Management Plan which encourages waste reduction. In 2003, Louisiana had 155 hazardous waste sites, 13 of which were included on the National Priorities List, included in the Environmental Protection Agency's database. Of the total river miles in the state impacted by pollution, 69% of the pollution is due to nonpoint sources such as agricultural and urban runoff. Efforts by DEQ to curb nonpoint source pollution have included the support and cooperation of the agricultural community and other state and federal agencies.
Among the most active citizen's groups on environmental issues are the League of Women Voters, the Sierra Club (Delta Chapter), and the Louisiana Environmental Action Network (LEAN). Curbside recycling programs exist 28 parishes. In 1996, wetlands, which once covered more than half the state, accounted for about one-third of Louisiana's land. In 2001, Louisiana received $68,112,000 in federal grants from the Environmental Protection Agency; EPA expenditures for procurement contracts in Louisiana that year amounted to $69,000.