If you manage water assets such as lakes, rivers, canals and ponds, then you will know that warm summer weather conditions can pose particular problems
for fish and aquatic life. As water temperatures increase, changes can occur in water systems which can cause stress and even death to those creatures
living within them. Mike Hill is an experienced aquatic ecology specialist at Thomson Ecology. Here he looks at some of the issues that might arise
in managed water bodies and how to prevent them.
Managing water assets can be a difficult business. There are many things that can go wrong and a level of expertise is required to successfully manage
them. If left, the issues that are most common in water bodies are often seen in combination and can cause serious problems for fish and other aquatic
life. They can also be unsightly and present health and safety risks for people and animals, and present a cost burden for those managing water bodies,
so it is important to be aware of the issues, and how to prevent or tackle them. Some of the main issues that arise as temperatures heat up in summer
- Temperature – the warmer the water, the less able it is to carry dissolved oxygen. Higher water temperatures increase respiration rates in fish and
other aquatic animals, and the toxicity of certain pollutants (such as heavy metals) to aquatic life.
- Algal blooms – warm conditions speed up the growth of algae and other aquatic plants, often turning the water green. This is especially a problem where
there are excessive nutrients available in the water (from point-sources, such as run-off or discharges, and diffuse sources, such as the breakdown
of organic material) and these can result in a series of impacts on water quality and aquatic life.
- Dissolved oxygen – a knock-on effect of high levels of algae and aquatic plant growth within waterbodies is that fluctuations in dissolved oxygen may
be caused during the summer months. These fluctuations can be extreme in very hot, sunny conditions, and can cause ‘super-saturation’ of dissolved
oxygen during the day, and severe oxygen depletion at the end of the night, when fish can sometimes be seen ‘gasping’ at the water surface.
- Algal ‘Crash’ – occasionally, certain conditions such as rapid changes in temperature or atmospheric pressure can lead to sudden algal die-off, which
is sometimes referred to as an algal ‘crash’. The microbial breakdown of this dead plant material uses oxygen and can cause the dissolved oxygen
of the waterbody to become lowered or depleted (anoxic). This sometimes results in the water appearing black, and hydrogen sulphide may be produced
under these conditions (with an associated smell of rotten eggs). These conditions are clearly harmful to aquatic life, and physical aeration or
dosing with hydrogen peroxide may be required to restore and maintain dissolved oxygen levels during these events.
- Blue-green algae (cyanobacteria) can also proliferate in the summer months and large accumulations can cause toxins to be produced which can be dangerous
to animals and humans if they are ingested, and can also cause skin irritation. This is a particular problem in waters where swimming and other
water sports take place.
- Water levels – some watercourses can dry out altogether, or become pooled, causing stress and mortality to aquatic life.
- Less dilution for pollution – with lower river flows, or reducing water levels in still waters, the impact of any polluting discharge is often worsened
due to the lowered dilution potential and a temperature-related increase in toxicity of certain pollutants, increasing stress and the likelihood
of mortality of aquatic organisms.
- Disease and parasites – Increasing water temperatures can be triggers for disease outbreaks, particularly in fish. Reductions in water levels in still
waters can also temporarily increase fish densities (by reducing available space), which also increases the chances of the spread and proliferation
of aquatic pathogens and parasites.
There are steps you can take to ensure that your water assets remain healthy.
- Implement a regular water-quality monitoring programme to keep your facility in a healthy condition.
- Obtain baseline ecological information with the help of an aquatic expert to understand the potential risks and the value of your assets. This will
be important in validating any subsequent insurance claims should you lose fish stocks or other aquatic life.
- Monitor likely long-term weather conditions. If a hot spell is forecast, then ensure that your facility is ready to cope and keep it well monitored
throughout a dry period.
- Consider pre-emptive fisheries management. By keeping fish stocks at sensible levels, you will ensure that your facility is not overstocked and prevent
- Be able to identify early signs that a problem is developing and take pre-emptive action.
- Develop a response plan with an aquatic management expert to include assessment and remediation options.
- Regularly review and adapt your plans to address changing conditions.
With regular maintenance and a structured plan in place, you should be able to pre-empt problems and ensure that people share the pleasure that natural
water features can bring.
Our aquatic ecology team is able to help with all aspects of aquatic monitoring, management and remediation. Please contact us at 01483 466066 or email
[email protected] for advice.