If you've ever been in the water around Hobart, you probably came close to a number of jellyfish but would never have known it.

While the waters around Tasmania are too cold for many of the larger, more well-known jellyfish, there are still plenty of tiny ones to keep expert Lisa-ann Gershwin very busy.

"A couple of weeks ago we were out here and we found three new species in about 10 minutes of sampling," Dr Gershwin told Sarah Mashman on ABC Radio Hobart.

Obelia jellyfish look a bit like a child's drawing of the sun and are common in the River Derwent. ( Supplied: Lisa-ann Gershwin )

"We're not looking for big old whopping jellyfish, the type you usually see; we're actually looking for the little micro-medusae [jellyfish]."

Dr Gershwin fishes for the micro-jellies just metres from her lab at the CSIRO in Hobart, simply dipping her plankton net into the River Derwent at the wharf.

"It looks a bit like taking your shark for a walk," she said about walking up and down the wharf to catch jellyfish.

Dr Gershwin named this micro-jellyfish Sphaeronectes tasmanica. ( Supplied: Lisa-ann Gershwin )

"When I do this, every single time I pull the net up it feels a bit like Christmas morning, seeing the Christmas tree glittering and you have no idea what's in those wrapped, ribboned, decorated boxes, but you know you're going to love it."

Dr Gershwin really loves her work and really loves jellyfish.

She has discovered and classified more than 200 species, from the big blobbing things to ones so small you can barely spot them with the naked eye.

Csiromedusa medeopolis is a micro-jellyfish named after the CSIRO. ( Supplied: Lisa-ann Gershwin )

"I've been working with the Tasmanian jellies for over 20 years," she said.

"Even when they're little tiny guys you tend to know them as old friends, and when you see them it's, 'Oh look, it's so-and-so'."

Using a clear plastic bowl, small spoons from airline catering and an eyedropper, Dr Gershwin carefully looks through her catch of microscopic creatures to spot any jellyfish.

"I always wear dark pants when I'm sampling," she said.

"Because the clear bowl against a dark cloth background, the clear bowl turns into a mirror and you get a really amazing view of everything.

"We look for things that are pulsing because that's a dead giveaway, but we also look for anything that's kind of circular.

"It's kind of the luck of the draw when it comes to jellyfishing."

While finding new species is always exciting, Dr Gershwin said she was happy spotting even the most common of the miniature creatures in her bowl.

Solmundella is one of the many species described by Dr Gershwin. ( Supplied: Lisa-ann Gershwin )

On a recent fishing trip with the ABC she pulled up an Obelia, a common type of micro-jellyfish found in the Derwent.

"Hello, baby. Isn't he cute?" she said, spotting the millimetre-sized marine animal.

"He's a little round, disc-looking guy and he's got four little round gonads or reproductive organs and a little mouth in the middle, so he looks like the five spots on a die.

"They're normal here. They're so cute. I just love them."

A new species of ectopleura found by Dr Gershwin. ( Supplied: Lisa-ann Gershwin )

Dr Gershwin's passion for all things jellyfish is shared with the public through the Jellyfish App, a mobile program that helps people identify different species and includes a way to contact Dr Gershwin directly.

"I'm happy to share my jelly world," she said.

"I pinch myself every time I stand in this lab and I pinch myself every time I've got my plankton net in my hand ready to throw it in and see what comes back up.

"I just feel so lucky, so unbelievably lucky doing something that I love so much."