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Why Are Pond & Lake Water Levels So Low?
Across the UK, we're seeing ponds and lakes at exceptionally low levels following prolonged periods of dry weather and limited rainfall. In some cases, customers are reporting water levels several feet below normal.
While the lack of rainfall and reduced groundwater or surface-water recharge are often the main causes, these unusually low levels are also exposing problems that have been developing within ponds for many years.
Heavy silt accumulation, excessive reeds and aquatic vegetation, and established self-seeded willow can all affect the depth, capacity and long-term resilience of a pond or lake.
Why is my pond water level dropping?
All ponds naturally gain and lose water throughout the year.
During warmer weather, water is lost through evaporation, while surrounding trees and vegetation also draw water from the ground and pond margins through their root systems.
Normally these losses are replenished by rainfall, groundwater, springs, ditches or surface-water runoff.
Following prolonged dry weather, however, groundwater levels can fall, springs and ditches may provide less water and there simply isn't enough incoming water to replace what is being lost.
This can result in a significant reduction in pond and lake water levels.
Can willow trees affect pond water levels?
Willow naturally thrives around ponds and wet ground, and self-seeded trees can quickly become established if left unmanaged.
As they mature, willows develop extensive root systems and can draw significant quantities of water from wet ground and pond margins during the growing season.
A few willow trees shouldn't be blamed solely for a pond losing several feet of water. However, where a number of trees have become established immediately around a pond, they can contribute to the overall water demand during prolonged dry periods.
They also introduce leaves, branches and other organic material into the water. Over many years, this decomposes and contributes to the accumulation of sediment on the pond bed.
For ponds intended to remain predominantly open water, managing unwanted self-seeded willow can therefore be an important part of long-term maintenance. Specific tree's can draw many 100's of liters per tree per day!
Do reeds and pond vegetation use water?
Yes. Reeds, bulrushes and other emergent vegetation draw water through their roots and release it through their leaves in a process known as transpiration.
Healthy marginal vegetation is an important part of a pond ecosystem and provides valuable habitat. Problems occur when it is allowed to spread unchecked and begins occupying a significant proportion of the pond.
During dry conditions, extensive vegetation adds to the overall water demand while also progressively reducing the amount of open water.
Aquatic plants such as water lilies and submerged weeds also form part of the pond ecosystem. Their effect on water loss is more complicated - for example, lily leaves can shade the water and reduce some direct evaporation - so aquatic vegetation shouldn't simply be blamed for falling water levels.
However, excessive aquatic growth is often associated with increasingly shallow, nutrient-rich ponds and can be an indication that management is required.
How does silt affect pond water levels?
Silt doesn't consume water, but it can dramatically reduce the effective depth and water-holding capacity of a pond.
Over many years, leaves, decaying vegetation, soil and organic matter accumulate on the pond bed.
A pond that was originally 1.5 metres deep may eventually contain a substantial layer of soft sediment, leaving considerably less actual water depth above it.
This often goes unnoticed while water levels are normal.
During prolonged dry weather, however, falling water levels can expose just how much of the original pond depth has already been lost.
A deeper pond has considerably more water available before falling levels become critical, whereas a heavily silted pond can become extremely shallow or expose large areas of the bed much sooner.
Low water levels can expose an existing problem
One thing we're increasingly seeing is that exceptionally low water levels are revealing problems that have potentially been developing for decades.
Large areas of accumulated silt become visible, reed beds extend much further into the pond than previously realised, and areas thought to contain reasonable water depth can turn out to be predominantly soft sediment.
In these situations, the dry weather hasn't necessarily created the underlying problem - it has exposed it.
This can also provide a useful opportunity to assess the condition of a pond and determine whether restoration work is required.
Can pond maintenance help?
No amount of pond maintenance can replace rainfall, raise groundwater levels or guarantee that a pond won't experience low water levels during another exceptionally dry year.
However, appropriate management can restore lost depth, maintain open water and improve the overall condition and resilience of an ageing or heavily overgrown pond.
Depending on the site, restoration works may include:
Desilting to restore lost depth and water capacity
Reed and bulrush removal
Aquatic weed and vegetation clearance
Selective removal of unwanted self-seeded willow and scrub
Restoring areas of deeper open water
The objective isn't to remove all vegetation. A healthy pond should contain a mixture of open water and suitable aquatic and marginal habitat.
The aim is to prevent uncontrolled vegetation and sediment accumulation from gradually transforming an open-water pond into an increasingly shallow and heavily vegetated wetland.
Is your pond becoming increasingly shallow?
If this year's dry conditions have resulted in unusually low water levels, it's worth looking at what has been exposed.
Deep accumulations of silt, extensive reed growth, excessive aquatic vegetation or established self-seeded willow can all indicate that a pond would benefit from restoration or ongoing management.
At Simply Aquatic, we undertake pond and lake restoration throughout the UK, including pond and lake desilting, reed and bulrush removal, aquatic vegetation clearance and silt management.
If you're concerned about low water levels or the condition of your pond or lake, send us some recent photographs of the site and we can provide an initial assessment and discuss the most appropriate options.
