Tim the Yowie Man: looking for the chill factor as Canberra weather heats up

Over summer, the Senior Research Fellow with the Institute for Applied Ecology at the University of Canberra divides her time between sitting in front of her computer and splashing around in our rivers and lakes. The latter, all for "research purposes", of course.

So, when earlier this week, this column received a query from Tom Wood, of Kaleen, asking if Canberra's scorching start to 2017 has affected the water temperature in our rivers, I promptly arranged to meet Dyer at one of her favourite haunts, the Murrumbidgee River at Uriarra Crossing. If anyone would know the answer to Wood's question, it would have to be Dyer who recently completed a study of Murray Cod habitat which included monitoring water temperatures at numerous points along the 'bidgee for the last three summers.

I arrive at the riverside recreation area just on midday, and being a weekday, but for an elderly couple reading books under the shade of casuarina, Dyer is the only one here. Or at least I think she is. Her vehicle is in the car park, but I can't find her.

Perhaps she's having a bite to eat on one of the many picnic tables spread along the river flats? No, she's not there either.

I eventually spot someone splashing around down in the shallows. I should have known!

Dyer is already cooling-off in her second "office".

Grabbing my water proof camera and trusty notebook, I scurry down to the river bank, where expecting the usual cold rush around my legs, I hesitantly edge into the water. But just as Wood had foreshadowed in his email, "the water is the warmest I've ever felt."

"Heck, it's like a bath!" I holler to Dyer as she pulls her giant-sized multi-probed thermometer out of the water.

"It's not that hot," I just hear her say over the sound of water cascading over an outcrop of semi-submerged rocks near me. Glancing again at her thermometer, she reports, "it's about 25 degrees in, and about the same out."

In order to get in closer earshot of Dyer, I creep towards the centre of the pool, and while trying to keep dry from the knees up (What columnist in their right mind wouldn't wear swimmers when covering a river?) almost drop my notebook in the process. "It's not all that bad", I think to myself as I perch myself on a rock which is both shaded by an overhanging tree and also sports a comfy flat top just poking out of the water — what a delightful spot to sit and to conduct an interview.

While it might be a warm 25 degrees in the water at this pool, according to Dyer, "there are some pools along the river where the water temperature is currently as high as 32."

"In fact, the water currently the hottest I've ever recorded," she says, confirming Wood's claims.

Dyer explains that while water temperatures along the stretch of the Murrumbidgee which flows through Canberra have a direct relationship with air temperature, "it can vary significantly depending on where and at what height in the water column the temperature is measured."

While it may be 32 degrees near the surface of a shallow pool, if you really want the ultimate cool-off then according to Dyer you need to "dive down to the bottom of the deeper pools, of which there are half a dozen in the ACT and where the water temp mid-summer in can be as low as 18."

"Anyone who goes for a swim in those deep pools will feel it, just drop your feet down and they can get quite cold," says Dyer who stays well clear of these pools during winter when the temperature can struggle to reach double digits." Brrr.

Apart from water depth, other factors which cause the river water to be cooler include riparian vegetation that shades the water and the presence of large rocks. "Water flowing over the rocks causes the water column to mix better," explains Dyer waving one of several dragon flies who have come to see what all the fuss is about, away from her face.

I end up chatting to Dyer for almost an hour during which time the expert freshwater ecologist shares all sorts of fascinating facts about the 'bidgee's water temperatures, including that "on really hot days you can get a cooling effect at the surface caused by evaporation which means that on a 38 degree day, water near the surface might actually be a bit cooler than on a 30 degree day."

I also manage to extract the all-important information for those of us wanting to cool-off this weekend — the location of those deepest pools. "There is an 8 metre-deep pool just a bit upstream of main swimming area at Kambah Pool and a 12 metre-deep pool a bit upstream of the island at Pine Island," she reveals.

Dyer does however, remain cagey about the exact location of the river's other deep holes, no doubt because they are prime habitat of the Murray Cod, a native fish species which she explains "don't like water that's too hot due to the lower dissolved oxygen content."

In the midst of this hot spell, we are lucky to be blessed with so many swimming holes in our region. However, with the high number of drownings in Australia this summer, please remember to take care in all our waterways. Oh and don't forget your togs.

So how do current water temperatures in the Murrumbidgee stack-up against other popular places for Canberrans to cool-off.

Murrumbidgee River: Ranging from18 at the bottom of deep pools and 32 in still, shallow water.

Dickson Pool: All three outdoor pools are heated to between 25 and 26 degrees, and according to pool managers "due to the record heat this summer, we are not needing to heat them as much as most years."

The south coast: The temperature range varies from beach to beach but is currently between 21-24 degrees. A spokesperson for the Bureau of Meteorology (BOM) reports that "the main factor that influences sea surface temperatures in NSW is the East Australian Current," adding "and the sea surface temperatures in the open ocean are currently between 1 and 3 degrees warmer than the average for this time of year."

Clue: Read all about it! Canberra's curious 'castellation'.

Degree of difficulty: Easy - Medium

Last week: Congratulations to Brayden Sorensen, of Dunlop, who was first to correctly identify last week's photo (inset), sent in by Elissa Bent, of Wagga Wagga, as the tidal sand bar in mouth of the Clyde River at Batemans Bay. Bent spent several weeks this summer kayaking to the bar, which is only exposed at low tide, with her family to play beach cricket.

Sorensen, a keen fisherman, who says nearby waters are "a great spot to snare a flathead or two", beat a number of other hopeful entrants to the prize, including John Perkins who thought it was "near Narrawallee", Alberta Hayes who guessed "Wollumboola Lake" and Martin Visser who was convinced that it was the photo featured "the entrance to Tuross Lake."

Meanwhile Phill Sledge, of Kaleen, who recently spotted a pirate flag fluttering on the sand bar wonders "if the vanishing 'island' has an official name.", adding "if not, perhaps it should be nick-named "Pirate Island.'

How to enter: Email your guess along with your name and address to timtheyowieman@bigpond.com. The first email sent after 10am, Saturday February 11, 2017 with the correct answer wins a double pass to Dendy cinemas.

CONTACT TIM: Email: timtheyowieman@bigpond.com or Twitter: @TimYowie or write c/- The Canberra Times, 9 Pirie Street, Fyshwick. You can see a selection of past columns online.