Strainer Danger: For Teachers
A strainer is an obstacle in the river that allows water to flow through it but stops larger solid obstacles.
Strainers are typically:
- tree branches or roots that are held in the river across the current
- construction debris like reinforced steel mesh
- collections of boulders
Strainers may be visible or fully submerged.
Swimmers can be trapped against strainers by the force of the river flow. They cannot get free and drown.
People do not recognise the danger strainers represent. They think they can easily swim over a strainer or move around it. They do not understand the force of the water that will trap them against the strainer.
The Be River Safe video section River Safety has a section called Strainer Danger.
In this section an experienced swimmer shows how to swim over a strainer or to swim up onto the top of the strainer.
This is theoretical knowledge only, no-one except the most experienced river users practise swimming over strainers. You will need to make a decision about whether to include this demonstration in your river safe programme.
If you are trapped by a strainer you will drown. Knowing what to do gives you the chance to recognise the danger and try to save yourself.
The footage does show that, while the flow of the river does not look particularly strong or rapid, the force of the flowing water will trap anyone swimming in the river against a strainer, or an obstacle like a rock.
- Be River Safe video
- Fact sheet: RIVER FEATURES – STRAINERS
- An activity about the danger of strainers
Discussion about the dangers of strainers can focus on:
- how dangerous strainers are
- the need for someone being swept toward a strainer to swim up as hard as possible to get over the strainer or up onto the strainer
- the force of the water that traps the swimmer against the strainer and makes it impossible for them to get away •why it is too dangerous for anyone other than an expert river swimmer to ever practise the skill of swimming over a strainer
- the safety precautions the group had in place when they filmed this dangerous sequence.