Florida’s Red Tide and Water Quality Crisis: What It Means for Coastal Wastewater Engineers

What does the science say about red tide and nutrients?

Red tide begins offshore, and land-based nutrients matter once a bloom comes inshore. The Florida Fish and Wildlife Conservation Commission's red tide overview describes four bloom stages: initiation, growth, maintenance, and dissipation or termination. Initiation happens in nutrient-poor water far from the coast. During maintenance, wind and currents move the bloom, and if it moves inshore, nutrient runoff from land may help it expand.

The stronger wastewater link is inside Florida's estuaries. Many Florida bays and lagoons do not meet nutrient standards. Many of those waters have nutrient TMDLs, and the state carries out the reductions through FDEP basin management action plans (BMAPs). A BMAP is the state's plan for reaching the reductions a TMDL sets, and FDEP says it is legally enforceable once adopted.

Where does wastewater add nutrients to coastal waters?

Through four pathways, and each one has an engineering fix:

• Septic drainfields, which pass nitrogen to groundwater as nitrate
• Leaking gravity sewers and manholes, which lose untreated wastewater to soil and groundwater
• Treatment plants that discharge effluent without a nutrient removal step
• Reclaimed water applied to land, which still carries the nitrogen and phosphorus the plant left in it

Wastewater is one source among several, alongside agricultural runoff, stormwater and atmospheric deposition. A credible plan estimates the wastewater share before it promises results.

Why are septic systems the first target?

Because there are a lot of them, and a conventional system removes little nitrogen. The FDEP Onsite Sewage Program estimates 2.6 million septic systems in operation in Florida, about 12 percent of the septic systems in the United States. FDEP has been responsible for the onsite sewage rules since July 1, 2021, and county health departments still handle routine permitting and inspection.

A conventional tank and drainfield is not built to remove nitrogen. Nitrate leaves the drainfield, moves with groundwater and reaches canals and bays. Where groundwater is shallow, that path is short.

The septic rules changed in 2023. Under HB 1379 (2023), as the Florida Senate's bill summary describes it, new septic systems are prohibited inside a BMAP, reasonable assurance plan or pollution reduction plan area where sewer is available. Where it is not, a new system on a lot of one acre or less must be an enhanced nutrient-reducing system or another system that achieves at least 65 percent nitrogen reduction.

The Indian River Lagoon goes further. FDEP's enhanced nutrient-reducing system guidance applies the requirement to new systems on lots of all sizes in the Indian River Lagoon Protection Program area from January 1, 2024. By July 1, 2030, existing systems there must connect to central sewer where it is available or upgrade to a system with at least 65 percent nitrogen reduction.

Septic-to-sewer projects are harder than they look. The new sewers have to fit established neighborhoods with mature trees and narrow rights-of-way. The receiving plant needs capacity for the added flow, or an expansion with its own FDEP permit. Flat coastal ground usually adds lift stations to the design.

How do leaking sewers add to the load?

Exfiltration sends untreated wastewater into the ground before it reaches the plant. Cracked pipe, failed joints and broken manholes leak outward wherever the pipe sits above the groundwater. Where groundwater moves quickly to surface water, that leak is a direct, untreated nutrient pathway.

The same defects let groundwater in when the water table is high. That infiltration dilutes the wastewater, uses up plant capacity and can weaken biological treatment. A collection system rehabilitation program that deals with both directions improves plant performance and cuts nutrient loss.

Do coastal treatment plants now need advanced waste treatment?

Many do, on fixed deadlines. Section 403.086, Florida Statutes, bars sewage discharges without advanced waste treatment into a list of named bays and their tributaries, including Tampa Bay, Sarasota Bay, Charlotte Harbor Bay and Biscayne Bay. The Indian River Lagoon and its tributaries are covered from July 1, 2025.

The 2023 changes reach much further. By January 1, 2033, the same requirement applies to discharges into waters that are not attaining nutrient standards or that are under a nutrient BMAP or reasonable assurance plan. Waters that reach that status after July 1, 2023 get 10 years from the determination. FDEP can require a stricter standard where a TMDL or water quality criteria call for it.

Advanced waste treatment has a number. Section 403.086(4)(a) defines it as treatment that produces reclaimed water meeting, on a permitted annual average basis, 5 mg/L CBOD5, 5 mg/L suspended solids, 3 mg/L total nitrogen and 1 mg/L total phosphorus. Secondary treatment designed only for BOD and solids leaves total nitrogen well above that.

Getting there usually means biological nutrient removal, plus chemical phosphorus removal and filtration where the limits demand it. Florida's numeric nutrient criteria, in Rule 62-302.531, F.A.C. and the estuary rule 62-302.532, help decide which waters are impaired for nutrients, and so which plants face the 2033 deadline.

Does reuse take a plant out of the problem?

Mostly, and Florida law now pushes plants toward it. Section 403.064(16), Florida Statutes, required utilities that discharge effluent to surface water to file a plan by November 1, 2021 to eliminate nonbeneficial surface water discharge by January 1, 2032. There are exceptions, such as a facility that reuses at least 90 percent of its annual average flow, and some small and rural utilities are exempt.

Reuse is not nutrient-free. Reclaimed water used for irrigation still carries the nitrogen and phosphorus the plant left in it. Section 403.086 now says that inside a nutrient BMAP or reasonable assurance plan area, reclaimed water used for irrigation or other land application must meet the advanced waste treatment nitrogen and phosphorus limits by July 1, 2034, where FDEP's plan finds that use is contributing to the impairment.

For a utility planning an expansion near the coast, my advice is to design for reuse from day one and size the nutrient removal for where the limits are heading, not only where they sit today.

What does this mean for coastal developers?

Water quality near your site is now a permitting variable. A project that adds wastewater in a watershed under a nutrient BMAP will face more scrutiny than one outside it. The wastewater plan, whether utility connection, private treatment or reuse, needs technical documentation of its nutrient load, not general assurances.

The limits of this post. It is general education on Florida rules as read in October 2026, not a permit determination. The legislature amends these sections often, and which deadline applies depends on your receiving water, your BMAP and your county. Confirm the current statute and BMAP text with FDEP before design.

Frequently asked questions

Does wastewater cause red tide in Florida?

No. FWC says Florida red tides begin offshore in nutrient-poor water. Nutrient runoff from land may help a bloom expand once it moves inshore, so cutting wastewater nutrients helps nearshore water quality, but it will not stop red tide from forming.

I run a small coastal Florida utility that discharges to a bay under a nutrient BMAP. Where do we start on the 2033 deadline?

Start with a nutrient mass balance: effluent monitoring data, receiving water flows and any other loads your system adds, such as collection system losses. That sets your baseline against the advanced waste treatment limits. Then compare the options together: biological nutrient removal, chemical phosphorus removal, more reuse and sewer rehabilitation. The result is a capital program you can take to FDEP for funding and explain to ratepayers.

We are developing coastal Florida lots under an acre with no sewer nearby. What wastewater options should we look at first?

First confirm whether the site is in a BMAP or other affected area and whether sewer is available. If it is, new septic systems are off the table there. If not, lots of one acre or less need enhanced nutrient-reducing systems. For a larger project, a private plant designed for nutrient removal, with on-site reuse, may be the better answer than many individual systems. Document the choice in your permit applications.

How do we tell if our sewers are leaking nutrients?

Flow monitoring at several points shows reaches where flow is lost between manholes. CCTV then finds the defects, and smoke or dye testing confirms the connections. Measured nitrogen and phosphorus concentrations turn the lost volume into a load estimate you can defend for capital planning.

Related resources

• FDEP Permitting for Wastewater Systems in Florida: A Practical Guide for Developers
• Florida's Advanced Wastewater Treatment Mandate: What AWT Requirements Near Impaired Waters and Springs Add to a Project's Treatment Design
• How to Navigate FDEP's OSTDS Upgrade Program: A Guide for Florida Property Owners and Developers
• Water Reuse in Florida: How the State's Progressive Rules Are Shaping Infrastructure Design

Planning wastewater work near a Florida bay or lagoon?

The rules now turn on your receiving water, your BMAP and your lot sizes. MES is licensed in Florida, and we sort out which rules apply, then design the work to meet them.

We specialize in:

• Nutrient loading analysis and nutrient reduction planning for coastal wastewater systems
• Septic-to-sewer conversion engineering and FDEP permitting support
• Collection system condition assessment and rehabilitation planning
• Biological nutrient removal and reuse system design
• Wastewater treatment feasibility for coastal Florida developments
• Capital improvement planning and funding application support

Modern Engineering Solutions, McKinney, Texas. Contact: (214) 833-6748 or mod-eng.com