This lesson focuses on a salmon as a parr in a river, tracing the development of a salmon from parr to smolt in the middle reaches of a river.

Lesson Objectives

To enable pupils to become more aware of the dangers and hindrances to a parr's growth in this section of a river. This lesson will also foster understanding of the importance of good river management and to demonstrate the interdependence of all species in and around a river.

Video: Lesson 4
Presentation: Lesson 4
Teachers Guidelines

Bradán’s story continues, this time from parr to smolt (early stages). The need for a safe and suitable habitat with lots of boulders and deep pools to hide in is emphasised.

The following dangers to parr are highlighted:

  • Fish and Predators
  • Organic pollution and how it can destroy life in a river
  • Cattle trampling down Riverbanks
  • Fish and Predators

    Pupils should consult a bird-spotting book to identify the dipper. Questions could be asked as to how the dipper got to know Bradán. What does a dipper eat and why does she stand on a boulder in the middle of a river?

    Organic pollution and how it can destroy life in a River

    The term pollution refers to any undesirable change in the natural quality of environment brought about by physical, chemical, or biological factors. Environmental pollution is a negative change in our surroundings due to direct or indirect activities of humans. The high rate of increase human population, rapid expansion in the industrial and urban activities and modernisation of agriculture has resulted in generation of high volume of waste material causing slow deterioration of valuable resources of biological productivity.

    Most fresh water pollution is caused by the addition of organic material which is mainly sewage but can be food waste or farm effluent. Sources of farm pollution include:

  • Pesticide
  • Animal carcasses
  • Organic manure
  • Slurry
  • Parlour/dairy/vegetable washings
  • Fertilizers
  • Waste milk
  • Sewage sludge
  • Silage effluent
  • Bacteria and other micro-organisms feed on this organic matter and large populations quickly develop using up much of the oxygen dissolved in the water. Normally oxygen is present in high quantities but even a small drop in the level can have a harmful effect on the river animals. Animals can be listed according to their ability to tolerate low levels of oxygen. In the following list, animals which indicate a high level of dissolved oxygen are at the beginning while animals indicating a low level of oxygen are at the end: stone-fly nymphs, mayfly nymphs, freshwater shrimps, freshwater hog lice, blood worms, tubifex worms and rat-tailed maggots. For more information about water pollution and its causes, please follow the link -

    The concept of silage and silage run-off is introduced. Hay is dried grass; silage is pickled grass. Both are used as fodder for cattle.Pupils are asked to do some calculations with silage run-off and realise what a toxin it is.


    How many litres of water would be poisoned by the following amounts of silage juice?

  • ½ litre
  • ¼ litre
  • 5 litres
  • 10 litres
  • For additional information about silage, silage pollution and silage leachate, please follow the link below on Silage.

    Cattle trampling down Riverbanks

    Bradán can swim downstream safe in the knowledge that there is clean water and plenty of vegetation to protect her. Sometimes IFI have to repair rivers and their banks if they are damaged by cattle trampling, construction and other types of erosion.

    The dangers of cattle trampling down river banks and the need for good fencing in these cases to create an ecological corridor for fish are also mentioned. To demonstrate this, teachers can show pupils before and after images (see below) of what can happen if cattle and sheep are not kept away from the riverbank. Questions that can be asked of the pupils when examing the images include

    Before Conservation and Management work
    1.  What have the cattle done to the riverbank?
    2.  How can this affect Bradán?
    3.  What can be done to improve this?

    After Conservation and Management work
    1.  Does the river look healthy?
    2.  Can the cattle get in?
    3.  Why would Bradán like to live here?

    They learn the importance of insects to a parr’s growth and why suitable vegetation is necessary for the development and survival of parr. A bug hunt could be carried out here.

    To help pupils understand these dangers, "before" and "after" pictures of conservation and management work can be shown to the class. The work of Inland Fisheries Ireland in the management of a river is obvious from these pictures and these can be pointed out to the children. The Glore river is a tributary of the River Moy. Work here included in stream vegetation removal, deflector-rubble mat construction, limited tree cutting & gravel tossing. The “before” and “after” pictures enable pupils to use their observational skills to see the changes and improvements carried out by Inland Fisheries Ireland in their conservation and management work.

    Before Conservation and Management Work on Glore River

    This image shows the Glore River, tributary of the River Moy, before any works were carried out

    After Conservation and Management of Glore River, carried out by Inland Fisheries Ireland

    This image shows Rubble Matting in the Glore River, tributary of the River Moy

    This image shows Paired Deflectors in the Glore River, tributary of the River Moy

    This image shows Alternating Deflectors in the Glore River, tributary of the River Moy

    Rubble mat – are longitudinal mats made of rocks. Designed to speed up the channel flow they mimic the effect of a riffle. This gives habitat for salmonids and it may also cause the scouring of a pool downstream.

    Deflectors - also called hard points or wing deflectors, are spurs of rocks/logs or gabions extended from the bank into the stream. They stabilise stream banks by directing current away from the banks, creating slack water adjacent to the banks and dissipating the stream's energy. They also add diversity to the channel by concentrating the flow and creating deep pools. Alternating deflectors in a straight channel can encourage a meandering pattern with a narrower, deeper flow. Double deflectors, spaced opposite each other, can cause a long, deep scour hole to form downstream.

    More information on stream management and stream enhancement can be found online at Ohio Stream Management Guide Publication

    Lastly, the pupils may use their knowledge and observational skills by exploring a picture of “Paradise” for a parr, see link below. Hopefully as they journeyed downstream with Bradán, they will be more familiar with the dangers and pressures on fish here.

    A Field Trip to test water quality is included. Indicator Species Chart will be helpful for this activity.

    Additional Teaching Material

    If food is scarce in a river, parr may stay three years in the river.

    Six – eight weeks before migration, a parr changes colour to silver and is now called a smolt. Smolts migrate to sea.

    Living organisms consist of organic matter (as do sewage, slurry and decaying plants). When dead or decomposing organic material enters water, bacteria multiply rapidly and may strip water of its entire oxygen content. This can kill many of the fish and other aquatic life forms living in the water.

    Slurry, silage run-off, discharge from sewage treatment works and some industrial outfalls are the biggest problems of the middle reaches of a river.

    Large numbers of cattle produce a lot of slurry. Slurry is a valuable fertiliser for land but a danger to rivers.

    Slurry should not be spread near a river when it is raining, wet or expected to rain. This increases the chance that slurry will run off either directly in the rivers/lake or indirectly through the soil which in turn runs into the river. Rain can also increase the amount of slurry running into a river, further damaging the water quality.

    If slurry, silage or sewage get into a river, they also cause a secondary problem by releasing nutrients such as nitrogen and phosphorus when broken down. Clean water already contains small quantities of these elements so extra nutrients speed up the growth of plants in the water. Plants need energy to function and in a process called respiration, they use oxygen to release energy. During the day, plants generate oxygen through the process of photosynthesis but at night they take the valuable oxygen from the water. The extra plants eventually choke the water and begin to die. As they rot, they are eaten by enormous amounts of bacteria, which further use up valuable oxygen that salmon require to grow and survive. This over-enrichment of water with nutrients is called Eutrophication. It comes from the Greek word meaning “to nourish”.

    Algal Bloom occurs when too much nourishment, e.g. domestic sewage, cattle slurry, pig slurry, silage juice, gets into a lake. It upsets the balance of growth in the water and is damaging to fish. On very calm days, tiny algae float to the surface and produce green paint-like scums (algal bloom) in enriched waters. Some are poisonous.

    Follow Up Work
    Aboriginal Fish

    Fish were a valuable food source for the Aboriginal people of Australia. They were great hunters and trapped fish in a variety of ways, from spears and traps to stunning them with poisonous leaves put into the water. Many of their paintings exist today. Aboriginals always used earthy colours got from natural dyes found in soil, blood, berries and insects. They always painted very simply in lines, spots and repeated pattern.

    'The Trout' by Seán Ó Faoláin

    Read the story 'The Trout' by Seán Ó Faoláin. A great story for language development, creative writing and poetry. Old-fashioned words like “ewer” need to be explained.

    At the end of the story

  •   Discuss with the class, the main points of the story.
  •   Ask pupils to write a passage on how the trout got into the well.
  •   Ask the pupils to describee how the trout felt as he swam to freedom.
  • Revision

    Two different types of revision material accompany this lesson; activity cards and whiteboard material.
    The activity card is a 4 page document that is filled out by the pupils to test their knowledge of the lesson taught. The teacher can decide if the activity card is filled out individually or in teams

    The whiteboard resource tests the pupils knowledge of the lesson taught. Pupils are encouraged to actively engage in answering questions relating to dangers to a parr, importance of good river management, and the interdepentance of species in and around the river.

    At the end of the lesson, Pupils should know
    How a salmon develops as a parr.
    The ideal habitat for a parr to survive.
    How to examine a river for pollution.

    1.  How a salmon develops as a parr.
    2.  The ideal habitat for a parr to survive.
    3.  How to examine a river for pollution.