It rained four days ago, and the pond behind your neighborhood is still holding water. The mosquitos have noticed. So have the homeowners, and now it’s on the agenda for the next board meeting: why is the pond full, is that normal, and whose job is it to do something about it?
Short version: if your pond was designed to be dry between storms, and most Front Range detention ponds were, standing water that lingers for days is a symptom of a real problem. It’s usually fixable, sometimes cheaply. But it’s also a compliance issue, because that pond is almost certainly a regulated stormwater facility that someone, probably you, is legally obligated to maintain.
First Question: Was It Designed to Hold Water?
Not every pond with water in it is broken. Some stormwater facilities, constructed wetland ponds and retention ponds with permanent pools, are designed to hold water all the time. If your community has one of those, water is the intended condition, and the questions are different.
But the workhorse facility on the Front Range is the extended detention basin, a dry basin designed to fill during a storm and then release that water slowly through an outlet structure. Under the MHFD criteria most local jurisdictions use, the water quality volume is designed to drain over roughly 40 hours. Give it a margin and the practical rule of thumb is this: a healthy dry basin should be empty within about two to three days of a storm. If yours holds water for a week, or holds water when it hasn’t rained at all, something is wrong.
If you’re not sure which type you have, the original drainage report or the facility’s O&M manual will say. Our guide to Colorado stormwater facility types can help you recognize what you’re looking at.
The Five Usual Suspects
1. A plugged outlet. The most common cause, and the cheapest to fix. Water leaves a detention basin through small, deliberately restrictive openings, an orifice plate, a well screen, a trash rack. Those openings clog: trash, cottonwood fluff, sediment, an overachieving beaver. When they do, the pond simply stops draining. Sometimes the fix is an afternoon with gloves and a rake.
2. Sediment. Every storm carries sediment into the basin, and over years it accumulates. Enough of it buries the lowest outlet openings, flattens the grading that was supposed to move water toward the outlet, and creates low spots that pond permanently. Sediment removal is a bigger-ticket item, but it’s also a maintenance obligation your facility documents almost certainly require at some threshold.
3. Groundwater and irrigation return flow. A Front Range specialty. A basin surrounded by irrigated lawns can receive a steady dry-weather trickle all summer, and in areas with shallow groundwater, the basin bottom may intercept the water table, especially once the basin has settled or been regraded. If your pond has a persistent wet patch that doesn’t track storms, this is a likely culprit, and it’s the one that most often needs an engineering evaluation rather than a shovel.
4. Vegetation. Cattails are both a symptom and an accelerant. They establish in standing water, then trap sediment and debris, which creates more standing water. A basin bottom that has gone fully to cattails is telling you it’s been wet for a long time.
5. A failed underdrain or clogged filter. Sand filters, bioretention areas, and some newer basins rely on water percolating through media into an underdrain pipe. When the media surface seals with fine sediment or the underdrain fails, the facility ponds. These failures are less visible and usually need a professional to diagnose.
Why Standing Water Is More Than a Nuisance
The mosquitos are the complaint you’ll hear first, and in Colorado, where West Nile virus is a real seasonal concern, they’re a legitimate one. But there are two bigger problems sitting under that water.
The first is capacity. A basin that’s already partly full, whether with water or with sediment, has less room for the next storm. That’s a flood risk to the properties downstream, and the whole reason the basin exists.
The second is compliance. That pond isn’t landscaping. It’s a permanent stormwater control measure, built as a condition of the development’s approval, and it comes with a recorded operations and maintenance obligation that runs with the property. Counties and municipalities along the Front Range operate post-construction stormwater programs that inspect these facilities, or require the owner to submit periodic inspection reports. Standing water in a basin designed to be dry is one of the most common inspection findings there is, and jurisdictions typically enforce it through an escalating ladder: a friendly reminder, then a formal notice with a deadline, then penalties. The board that responds at the reminder stage spends a fraction of what the board that responds at the penalty stage does.
Whose Problem Is It?
Usually yours, if “you” are the HOA, the metro district, or the commercial property owner the facility was conveyed to. The answer is written down: the plat, the drainage easement, and the recorded maintenance agreement for the development say exactly who is responsible for the facility. It is almost never the city or county, and the developer’s responsibility typically ended at turnover.
Boards are often surprised by this, because nobody handed them the paperwork when they inherited the pond. If that’s your situation, our article on what HOA boards inherit with a detention pond covers how that responsibility lands and what it exposes the board to.
What Fixing It Costs
It depends on which suspect you’ve got, and the range is wide:
Clearing a plugged outlet is the good news scenario: often a few hundred to a few thousand dollars, sometimes just labor. This is why regular inspections pay for themselves; a plugged trash rack found in April is trivial, and the same rack found during a July cloudburst is an emergency.
Sediment and forebay cleanouts run from the low tens of thousands up, depending on volume, access, and disposal. Unpleasant, but predictable and plannable. Our breakdown of what a detention pond actually costs over 20 years puts real numbers on this.
Chronic groundwater or a failed underdrain needs an engineering evaluation before anyone can price a fix, because the right answer might be an outlet modification, an underdrain repair, or accepting a wet-bottom condition and formally reclassifying how the facility is managed.
The most expensive option, reliably, is doing nothing until your jurisdiction finds it for you or a storm finds the downstream neighbors.
What to Do This Week
Look at the outlet. After the next storm, or now, if the pond is holding water without one, have someone look at the outlet structure and photograph it. Don’t send anyone into deep water or a confined space; photos from the bank are enough to start.
Find your paperwork. The drainage report and O&M manual for your development are public records; if they’re not in your files, your municipality or county has them. They tell you what the pond is, how it’s supposed to behave, and what maintenance you’re on the hook for.
Get a professional inspection. A qualified inspection will identify which of the five suspects you’re dealing with, document the facility’s condition, and give you a prioritized, priced list of what actually needs to happen, which is exactly the document a board needs to authorize spending. It’s also the report your jurisdiction wants to see. That’s a service we provide across the Front Range, with reports signed by a licensed Professional Engineer and formatted for submittal to your jurisdiction.
Write it down. Whatever you find and whatever you do, document it. A dated photo log and inspection record is the difference between a board that can show it acted responsibly and a board that can’t.
A pond that won’t drain is trying to tell you something, and it’s usually something small on its way to becoming something expensive. The boards that come out fine are the ones that listen early.