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Last week I mentioned the Ten Most Wanted, a list compiled by the of the most dangerous species threatening our waterways and this week, I actually got to see one of them in action.

I took the children on a canoeing trip along the Teifi (it's a seven week summer holiday, which means lots of activities are a must).

The Teifi gorge is one of the best examples of tidal gorge in the whole country and has been an important centre of coracle fishing and slate quarrying for hundreds of years, but now the gorge forms part of the Teifi marshes nature reserve.

Canoeing on the river.

Our expedition would take two-and-a-half hours and was thankfully instructor-led. We set off shakily from the Welsh Wildlife Centre at Cilgerran, getting used to the paddles and more importantly, the steering, but the water was like a mirror, calm and smooth.

All along the banks, we saw a pretty, innocuous-looking tall, pink flower which the instructor, Rhys, told us, used to be known as 'poor-man's orchid'.

But this was actually Himalayan balsam, a relative of the busy lizzie and the tallest annual plant in the UK, reaching heights of up to 3 metres.

Himalayan balsam has pink flowers and resembles the sweet pea.

It was first introduced into the UK in 1839 and 'escaped' from gardens, taking up residence mainly along riverbanks and marshland.

It's subsequently become a major problem, mainly because each plant can produce around 800 seeds a year, which contain explosive pods.

These can throw seeds up to 7 metres in all directions, allowing the plant to spread quickly, smothering all other vegetation as it goes.

According to the , it also suppresses the growth of native grasses and flora which weakens habitats and leads to erosion of the banks.

This in turn has a knock effect on the wildlife that inhabitant the river bank such as small mammals and birds who rely on native plants to provide food, shelter and habitat.

So, it just goes to show that something you could easily overlook as simply being 'pretty' can do so much damage to the eco-system.

Looks can be deceiving - Himalayan balsam growing along the river bank.

Getting rid of it is no mean feat either. Apart from chemical intervention, the only other option is to pull or cut the plants before they flower each year in June.

Apparently, there are even 'Balsam Bashing' parties held by some of the conservation authorities to clear the weed from the riverbanks. It all made for a sobering thought as we paddled our way down stream.

The canoe was a great vantage point to see the wildlife from though - a pair of heron seemed to be following us along our journey, a buzzard flew overhead and twice we saw fish leap energetically out of the water. It happened so quickly that it was difficult to identify them, but we decided it was probably sewin/ sea trout.

At the half-way point, there were the beginnings of 'when are we turning back?' and 'my arms are aching' from the children, but luckily the river did most of the work on the return journey - effortlessly guiding us back to our starting point.

We arrived back with aching shoulders, but as dry as when we started with all the paddles intact - so all in all, not a bad way to spend a day on the water.

If you fancy having a go, you can visit the canoe centre on the river at the Teifi Marshes Nature Reserve, Cilgerran, Pembrokeshire, SA43 2TB or at the Cardigan Bay Active Booking Centre on Teifi Wharf (by the old bridge in Cardigan Town), Cardigan, Ceredigion SA43 3AA. Telephone: (01239) 612 133.