If you are planning a trip to the South Island of New Zealand this summer, then this article is a MUST READ. Things have changed: due to biosecurity requirements all tackle, footwear, and nets are subject to rigid inspection on re-entry to Australia. If incoming gear is not clean and dry, owners can face possible confiscation with return after any treatment being at an owner's expense.

It's been two years since I fished the South Island of New Zealand and in that time a deadly and ongoing change has come over some of the very best of the streams. There's been an invasion of a most unwelcome guest – a smothering algae named Didymo– and it looks as though it plans to stay.

Didymo Geminata notoriously known as Didymo is an algae that is present in many European, Asian and North American waters and is now moving progressing through most of New Zealand's South Island streams with astonishing speed.

In appearance it looks like a brown or brownish grey carpet covering the stream bed from edge to edge. When it has become really established there are often longish streamers of white. The stuff looks slimy, but it actually feels a lot like cotton wool.

The algae grows from a single microscopic cell – which can survive for considerable periods out of water – and was first noticed in the Mararoa River in Southland on it's first ever appearance in the Southern Hemisphere. It has since spread rapidly from river to river despite determined efforts of NZ authorities to curb its growth. It's insidious stuff: a microscopic diatom that gives no hint of it's presence until it colonizes sufficiently to bloom into the characteristic carpet like growth spreading over the entire bed of even a fast flowing stream. Fast water does not slow the algae down, on the contrary it thrives.

At this point in time it has not taken hold in North Island waters although – ominously – dead cells of Didymo have been detected in some of the better streams. It’s there but not taking hold: the time bomb ticks.

The proliferation within the South Island doubtlessly lies with the plentiful New Zealand ducks and wading birds. While anglers are required by law to check, clean (soak in 5% dish detergent solution) and thoroughly dry gear before moving to another waterway there is no way of controlling water fowl movement so it's inevitable that further outbreaks will be wafted aloft on webbed feet. This algae grows from a single microscopic cell and survives for days out of water.

I recently fished the Twizel area and found Didymo in the major rivers. Imagine, no river gravel or stones, instead just a tatty carpet. The beautiful Ahuriri, the Tekapo, the Twizel; all were severely infected. So much so that the traditional indicator nymphing technique was virtually useless. The Didymo snagged the nymphs as soon as they got down and the indicator bobbed uselessly. I had heaps of practice strikes and lots more practice at removing Didymo from the nymphs after each cast.

Dry fly fishing or a dry as an attractor with a nymph under it was the alternative for us where Didymo was rampant. Fortunately the pest has not spread to the very upper reaches of some of the rivers – yet – and we were able to move to the smaller sections where the beds were clear of the stuff. On the down side, the fish tended to be a whole lot smarter and line shy in the small water situation.

Where this sorry saga is going to end is debatable. I imagine it will spread throughout South Island waters as a whole. Another problem occurred to me when I lifted a river stone in clean, unaffected waters I found upwards of a dozen mayfly nymphs scrambling out of sight; in Didymo covered areas I lifted a dozen rocks to find not one nymph. Therefore, how is this going to impact on fish quality, given that a trout's diet comprises 70%, or more, of nymphs and other invertebrates?

As can be imagined we don't want Didymo in our home waters and the Australian Quarantine and Inspection Services (AQIS) are doing their utmost to prevent its entry into Australia.

Used fresh water fishing equipment is scrutinized intensely after arrival from New Zealand and if any item is showing the slightest trace of dampness or foreign material it will be confiscated on the spot and treated with dipping, heat treatment or stored at – 18C for 24 hours. The AQIS staff are obliging but if several items require treatment they will be taken away and returned at owner's expense or as per arrangement for collection at a later (can be weeks) date.

Felt soled shoes are the worst: these items – being categorized of medium porosity – need to be completely dry for 48 hours prior to entry within Australia and if not will be certainly retained for treatment.

As my canvas landing net sheath was damp all of our tackle was taken and dipped, the G.Loomis rods removed from their travel packs and all sections treated. Thankfully, no rod tips were damaged in the process and as there were but two of us we were able to wait for an extra hour at the airport and eventually take the gear away with us.

Jet lagged travellers will hardly grin at the prospect of an extra hour delay at the airport. So look very closely at compliance conditions well before returning home and ensure nets and sheaths are totally dry and without the slightest bit of foreign matter. Wash rods down with mild detergent and dry the handles well. Footwear should be totally dry and utterly clean.

Felt soled boots, used for wading, are worst when it comes to decontamination. AQIS state, and I quote, "As it is not possible to determine whether such items (wading boots) are completely dry treatment is mandatory at certified premises at the importer's expense."

In New Zealand it is even more stringent. Fish and Game New Zealand are requesting anglers NOT to use felts if it can be avoided. Their advice is to use them only once after arrival and then "leave them at home."

Accordingly, I opted for a pair of Snowbee XS Pro Wading Boots as an alternative to the outlawed felts.

I chose the Snowbees because they really do look the part and are very sturdy. I also liked the concept of cleated rubber soles as I enjoy tramping paddocks on the way to the water. In practice I found them great for scrambling up or down steep rocky or wet banks and when wading about to fish I had no dramas with grip on some of the slippery rocks. Rubber can never be as effective as felt, true, but felt's finished.

The Snowbees were very light, had great ankle support, and I was able to give them a good pre-departure clean up with some detergent and a scrub brush. With synthetic uppers and rubber soles they easily dried out in the day prior to arrival at Brisbane International airport. Best of all they are not expensive in comparison to some of the U.S equivalents.

After 12 days of heavy fishing in the South Island my Snowbees look just as good as they day I first put them on, which is a sure sign of a good product.

Keeping Didymo out of Australia is vital and we can all play our part.

At least one day prior to departure from New Zealand allow time for the clean, check, and dry routine. Clean up well in advance with a good soaking in 5% detergent solution, check thoroughly for any adhering matter, and make sure everything is thoroughly dry before presenting it to an AQIS officer at the airport for inspection.