Before we dive in, I want to talk about something that I know many of you can relate to right now.
For years you’ve been getting an annual lake report that tells you everything looks fine on the surface, but then, out of nowhere, a toxic algae bloom shuts your beach or lake down.
Or invasive weeds just keep on invading even though you are nuking the lake with biocidal chemicals to kill them. Because so many lakes are ticking timebombs, loaded with problems no one notices until it’s too late.
Or maybe your lake management plan involves treatments like algaecides, herbicides or even alum and you’ve found that, despite your best efforts, the same problems keep coming back year after year. And the cost of those treatments keeps going up every year.
It’s frustrating, and it’s exhausting. It can make you feel like you’re stuck on a merry-go-round that you just can’t escape from.
You’re not alone.
In 2022, the Government Accountability Office released a report that echoed what so many of us have been subconsciously realizing. After decades of research and millions of dollars spent on studying the symptoms of lake decline, we’re still stuck in the same place, treating the symptoms instead of getting to the root of the problem.
That’s exactly why we’re here today.
This video series is designed to help you look below the surface and understand what’s really happening in your lake, rather than just what’s visible on your lake. We’re here to Simplify the Science of lake management, to cut through the confusion of long-winded reports, and to show you what really needs to be measured to understand your lake’s risk profile and status.
I’m Dave Shackleton, and these Simplify the Science videos will help you cut through the confusion of long-winded lake reports, understand what the Government Accountability Office highlighted in its 2022 report about why current practices are falling short, and show you how to use the right data to measure what matters so you can make better decisions that will save your lake and your lake lifestyle.
We’ve explained the three root causes that have to be tackled:
We will be doing a separate video on Measuring What Matters for each.
In this video, we’re going to focus on hypoxia, what it is, how it happens, why it matters, how to measure it, and what you need to see to be sure hypoxia has been eliminated from your lake.
I’ll also explain how you could be spending good money on making hypoxia worse and actually lighting the fuse on the time bomb at the bottom of your lake without realizing it.
And at the end I’ll tell you about the unseen shift we’ve noted in lakes across the country that could be pushing thousands of them into long-term failure.
So, let’s start by talking about hypoxia and why it’s such a serious threat to your lake’s health.
The EPA defines hypoxia to be when dissolved oxygen levels in the water drop below 2.5 milligrams per liter. But it’s more than just a technical definition. Oxygen is the lifeblood of your lake. Without it, every part of the ecosystem that naturally supports a healthy lake begins to collapse. Below 3mg/l fish start to be stressed.
When oxygen levels fall too low, the beneficial algae that help sustain the food web are overwhelmed by harmful cyanobacteria. Zooplankton die off, fish begin to suffer, and the entire food web starts to unravel.
It usually begins with algae blooms and invasive weeds. They grow rapidly when conditions are right, then die and sink to the bottom, where they decompose. This decomposition uses up oxygen, especially in the deeper, colder parts of the lake, creating hypoxia.
Because cold water is denser than warm water, and hypoxic water is denser that oxygenated water, gravity causes it to settle at the bottom, trapping itself beneath warmer, better oxygenated layers and holding it there. Over time, that bottom layer becomes permanently hypoxic, and slowly expands upward as more organic matter settles and decays, extending the dead zone further up into the lake.
From the surface, it might look like everything is fine. But beneath, your lake is slowly suffocating.
In a healthy lake, algae aren’t a nuisance, they’re an essential part of the ecosystem. They feed zooplankton, which in turn feed fish. Those fish then become food for birds, reptiles, and mammals. That’s the food web, and it’s what clears nutrients from the lake and keeps your lake balanced.
Every link in that chain depends on oxygen.
When oxygen levels drop, zooplankton populations start to collapse. Without zooplankton to feed on the algae, algae blooms can grow unchecked. Fish lose both the oxygen-rich water they need to breathe and the zooplankton they rely on for food.
It creates a vicious cycle, one that accelerates the collapse of the entire food web.
And the problems don’t stop there.
When the upper layers of sediment become hypoxic, benthic organisms, those tiny creatures at the bottom of the lake that consume organic muck, begin to die off.
So instead of being removed by the food web, nutrients get stuck in a perpetual recycling loop, fueling more algae, which die, sink, and decay, using up more oxygen and worsening the problem.
But it gets even more complicated.
This change in benthic oxygenation also disrupts the natural processes that keep nutrients locked in the sediment, causing them to be actively recycled back into the water instead.
Phosphorus is more soluble in hypoxic water, so it’s more readily available at the bottom of the lake. Ammonia levels also rise, which can be toxic to fish and provides another source of nitrogen that cyanobacteria can use.
Unlike beneficial algae that can only float at the surface, cyanobacteria have a unique ability: they can control their buoyancy. This allows them to dive deep to access nutrients from the sediment and then rise back up to the surface to get the sunlight they need to bloom.
That’s how they gain a competitive advantage, outcompeting the beneficial algae season after season. Eventually, that leads to the toxic blooms that can shut down your lake entirely.
That’s why tracking the profile of phytoplankton gives such valuable insight into your lake’s condition, but too few lake management plans do that in sufficient detail. But we’ll cover that in another video.
There’s an even deeper issue at play here, one that often gets overlooked.
Over the past several decades, as populations have grown and urban development has expanded, our lakes have been receiving more and more nutrient inflows. These nutrients come from a variety of sources: farm runoff, leaking septic systems, storm drains, and wastewater treatment discharges, just to name a few.
When those nutrients enter a lake they are captured by algae and transformed into biomass. Because there is too much algae for the food web to consume, the excess dies off and sinks to add to detritus and muck at the bottom. And once it has depleted oxygen and decomposed, that biomass is converted back into a nutrient stockpile rich in phosphorus and nitrogen.
All of that extra phosphorus and nitrogen acts like fertilizer for algae. When the algae bloom, the food web can’t always keep up. The excess algae die and sink to the bottom, where they build up over time.
That’s why, in addition to hypoxia and harmful blooms, many lakes have developed a sediment nutrient stockpile at the bottom.
So your lake can now drive its own decline from the inside, independent of nutrient inflows from the watershed. Even if you managed to block every bit of runoff from outside the lake, it has its own self-sustaining nutrient supply that keeps fueling its own problems.
So while reducing nutrient inflows is still important, it’s not the answer.
With all of that in mind, it’s easy to see how so many lake management plans go wrong.
They see weeds, so they spray them with herbicides.
They see algae, so they apply algaecides.
But even though the consequences are obvious, the inconvenient truth is overlooked or ignored.
When those plants and algae die, and I’ve said it a hundred times! – they sink and decompose, consuming even more oxygen from the water and adding more nutrients to the sediment.
At Lake Rogerene in New Jersey, we saw this firsthand. After just one herbicide treatment, the sediment depth increased by six inches across the entire lake. The eight-foot contour was nearly gone, and the seven-foot zone shrank dramatically. Oxygen levels plummeted.
Fortunately, Lake Rogerene had a RADOR oxygenation system in place, which allowed us to nurse the lake through the oxygen depletion and bio-dredge away that extra muck that the herbicide created.
But most lakes don’t have that safety net.
So is it really a treatment—or just a trick?
Like a magician’s sleight of hand, the problem seems to vanish before your eyes. The weeds wilt. The algae clears. Applause all around.
But it’s misdirection – the magician keeps your eyes trained on the surface, because while the surface looks better, the real damage happens out of sight, – on the bottom, where the dead biomass settles, oxygen is stripped away, and a new bloom is already being fed.
It’s not restoration. It’s illusion.
And unless you break the cycle, the final act is always the same: more muck, more nutrients, more blooms.
The question is, how long will it take you to see the difference between trick and treatment?
Let me share another real-world example with you.
There’s a 150-acre lake that was treated monthly with algaecide starting in early May. By late June, hypoxia had started at 32 feet. But what does that really mean? Just reporting the depth at which hypoxia occurs doesn’t tell you much.
In this lake it meant that about 15% of the water volume was hypoxic and 30% of the lake bottom was covered in hypoxic water – meaning that it was ground zero for nutrient recycling to keep the problem going.
So they kept treating with more algaecide.
By early August, just six weeks later, that hypoxic layer had crept up to 15 feet. That meant that the volume of hypoxic water had tripled – to 45% and more than 60% of the lakebed was covered by hypoxic water.
Selling all that algaecide is not good lake management. It’s slow-motion sabotage, it’s trick, not treatment.
When you measure what really matters and understand what’s going on beneath the surface, you can start to see why this happens and how to break the cycle.
So, how do you actually measure dissolved oxygen?
It’s simpler than you might think.
All you need is a dissolved oxygen meter. Lower it slowly into the water and take a reading at every foot, from the surface all the way to the bottom. Do this at the deepest part of the lake and repeat it every month.
First, note at what depth the dissolved oxygen levels drop below 5 milligrams per liter, that’s where the ecosystem begins to struggle. Then look for where it falls below 2.5 milligrams per liter, that’s where hypoxia takes over.
But those numbers alone aren’t enough.
You also need detailed bathymetric scans, underwater maps that show you the depth profile of the lake in 3D. This data lets you calculate how much of the water volume and the lakebed are affected by hypoxia.
Only with that information, can you truly understand the extent of the problem and begin to design a solution to fix it at the source.
That’s what how we design RADOR oxygenation systems.
When you restore oxygen throughout the water column, a lot of good things happen.
Phosphorus becomes locked in the sediment instead of leaching out.
Ammonia levels decrease, making the water safer for fish.
And cyanobacteria lose their competitive advantage, because they can’t dive for nutrients anymore.
With oxygen restored, the food web recovers. Zooplankton populations come back. They consume the algae. Fish can return to deeper waters. Nutrient recycling slows down.
And the lake stops fueling its own decline.
This is how you bring your lake back to life.
When you restore oxygen throughout the water column, a lot of good things happen.
Phosphorus becomes locked in the sediment instead of leaching out.
Ammonia levels decrease, making the water safer for fish.
And cyanobacteria lose their competitive advantage, because they can’t dive for nutrients anymore.
With oxygen restored, the food web recovers. Zooplankton populations come back. They consume the algae. Fish can return to deeper waters. Nutrient recycling slows down.
And the lake stops fueling its own decline.
This is how you bring your lake back to life.
Before we wrap up, there’s one more threat we need to talk about that we noticed in a lot of lakes across the country in the past few years.
Lakes naturally rely on seasonal turnover in the spring and fall to reset. This mixing process brings oxygen down to the bottom and helps flush out problems.
But warmer winters are interfering with that process.
Surface water doesn’t get cold enough to trigger the turnover.
In lakes that are over 60 feet deep, sometimes only the top 30 feet or so mix, leaving the bottom layers hypoxic year after year.
If your lake is over 15 or 20 feet deep, this matters a lot.
It means your lake might not be getting that seasonal reset anymore.
So the damage from hypoxia just keeps compounding over time.
I know this is a lot of information to absorb. Lakes are complex ecosystems, but the core principles are simple and absolutely critical.
Oxygen tells the truth about your lake. And measuring it is the first step toward bringing it back to life.
If you missed something, watch this video again. And if you want to dig deeper, download our free e-book, Simplify the Science.
In the next video, we’ll show you how to measure sediment reduction, bio-dredging progress, and shifts in phytoplankton populations, so you can get ahead of blooms before they happen.
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Together, we can bring our lakes and our lake lifestyle, back to life.
