Six dolphins and a possible two others have died since April last year.

While researchers have found how a number of them died through post-mortems, they are now investigating why so many died in such a short space of time.

Tourists to the region are set to increase in the next few months with the new highway bringing in visitors, summer approaching and cruise ships arriving.

Dolphin Discovery Centre general manager Jodie Mott said there was still plenty of dolphins keeping tourists occupied.

Ms Mott said until further test results were released, there was not too much to worry about and the majority of the population was healthy.

“There are no concerns for the bulk of the population but we need to check the health of the inner water dolphins,” Ms Mott said.

Murdoch University researchers with the South-West Marine Research Program found there was a wider population of about 200 dolphins in local waters and about 16 which used Bunbury inner waters regularly.

Since April 2008 to November 2009 six of the dolphins have been confirmed dead and another two have not been seen since August 2008 and April 2008 respectively.

The post-mortems revealed no clear trend in the timing of the deaths.

An investigation will now start to see if there are any connections with to the deaths of dolphins in the Swan River and if any contaminants were linked to the deaths.