Experts are pleading for a quick intervention after a baby dolphin was spotted in the Peel Inlet wrapped in fishing line this week while another Mandurah dolphin is still entangled after five months.
The calf called Jemo was spotted in the shallows of the Peel-Harvey estuary on Sunday with line wrapped through its mouth, ears, fins and all over its body.
Jemo's entanglement is so serious the Department of Biodiversity, Conservation and Attractions (DBCA) has promised it will try to free her in the next few days if weather conditions are suitable.
"Due to the ... impact on its health and welfare, the department will attempt to capture and disentangle the dolphin," a spokesperson told the Mail on Tuesday.
But newly mature female, River has a calf by her side and has been entangled since June and there are still no plans to try to free her, despite her deteriorating health.
Long-time Mandurah dolphin researcher Krista Nicholson says an intervention should have happened some time ago.
"It's good that they're doing something about it now but it's long overdue and absolutely unacceptable that we are not able to do better," Ms Nicholson said.
"It's been lingering on so long, it has really highlighted we don't have the preparedness to deal with these kinds of incidents."
A Mandurah Dolphin Rescue Project spokeswoman said she had hoped River would have been rescued by now.
"DBCA is putting a lot of resources and effort into it but at the same time we still haven't got to the rescue stage. It's frustrating but the most frustrating thing at all is that this shouldn't have happened in the first place."
The DBCA agrees there has been "some decline in River's body condition" but says she continues to swim freely and has been observed feeding and swimming fast in shallow water.
Also capturing a wild, free swimming dolphin in open water was complex and required specific circumstances to have any chance of success, the department said.
The operation was particularly complex due to the dolphin having a calf and the risks of a capture attempt to both dolphins, as well as the DBCA staff and volunteers involved in the operation.
"Careful planning and trialling of techniques is important to inform the capture operation."
Attempts to capture the dolphin to free it of the entanglement would be undertaken "if and when the opportunity presented itself".
The incidents highlight the hazards associated with discarded fishing line for Mandurah's 80 resident dolphins.
There is also concern about the economic impact - that the lower dolphin numbers would affect long term visitor numbers.
Mandurah Cruises director Myrianthe Riddy said it wasn't good for tourism and it wasn't a sight that visitors should be confronted with.
"River appears to be worsening," Ms Riddy said.
"We understand there are risks to an intervention but we should be taking these risks given the significance of this population."
When photos emerged of tightly wrapped baby Jemo, there was a strong emotional reaction on social media from local dolphin lovers, who are still reeling after Mandurah's resident dolphin calf Luca died in August last year after becoming entangled in fishing line for the third time.
And they expressed disgust that people were continuing to litter even though they knew the potential consequences.
"This is terribly sad that certain humans lack regard for how their activities affect these beautiful marine mammals," Julia Marina wrote on the Mandurah Dolphin Research Project facebook page.
"Fishermen need to be held more accountable somehow for the damage they cause through laziness and absolute lack of consideration."
The DBCA agreed that the entanglements were a timely reminder of the importance of disposing of fishing line - wich doesn't break down - and place appropriately in the Reel It In bins in the area.
If you spot a dolphin in distress contact Estuary Guardians Mandurah on their Facebook page or call the DBCA on 9219 9000.