Algal torch

A field instrument used to measure algal concentrations.

Catchment area

The area of land surrounding a body of water — including hills and mountains, woodlands, and built-up areas — from which precipitation (rain or snow) drains before flowing into a water body such as a loch, stream, river, or wetland.


A green pigment found in all green plants, including phytoplankton. It absorbs light energy from the sun, using a process known as photosynthesis, and converts it into energy for growth. Measurements of chlorophyll-a provide an indication of the amount of phytoplankton present in the water.

Clear Water Phase

A period in early summer when phytoplankton populations are drastically reduced due to high levels of grazing by herbivorous zooplankton (e.g. Daphnia). The clear water phase usually lasts two to three weeks, and ends when the Daphnia populations are reduced by lack of food or increased levels of predation


The process through which a body of water becomes over-enriched with nutrients (especially phosphorus and nitrogen), leading to excessive phytoplankton growth and the appearance of algal blooms.

Freshwater macroinvertebrates

Animals without a backbone that are large enough to be seen with the naked eye and spend part or all of their life cycle in flowing or standing waters. They include insects (fly nymphs and larvae, beetles and bugs), snails, mussels, leeches, worms, flatworms, slaters and shrimps. Freshwater macroinvertebrates are good indicators of water quality because different species have different levels of tolerance to pollution.


An essential nutrient for the growth of all living things, often added to farmland as a fertiliser to improve crop yields. Also present in animal and human waste.


An essential nutrient for the growth of all living things, often added to crops as a fertiliser to improve yields, as well as being used in various industrial processes. It is also present in animal and human waste.


Free-floating microscopic plants that are found throughout the world's waterbodies. They are a vital part of the food chain, performing the same role as larger macrophytes (underwater plants) and terrestrial plants in turning sunlight and nutrients into energy. However, when too many nutrients are available the phytoplankton can grow too fast, causing potentially harmful algal blooms.


An essential compound for the growth of diatoms, which are types of microalgae that are present throughout the world's waterbodies, both freshwater and marine. Diatoms extract dissolved silica from the water and use it to form a hard cell wall called a frustule.

Soluble Reactive Silica (SRS) is silica that is dissolved in the water, and therefore is available to be taken up and used by anything that needs it. Total Silica (TSiO2) is the concentration of silica present in the loch, in all of its forms.

Silicate (dissolved silica) concentrations are important, because a lack of silicate prevents diatoms from growing and allows other phytoplankton — especially cyanobacteria — to proliferate.


Microscopic animals that are present in most open water bodies. Zooplankton eat phytoplankton and are in turn eaten by larger animals, such as larger zooplankton, macroinvertebrates and fish.