A new report has warned of a toxic “ticking time bomb” of coal ash waste.

The report by Environmental Justice Australia says national guidelines are desperately needed and energy companies should be forced to maintain a bond or financial assurance to ensure ash dumps are properly managed.

“Coal ash is an enormous toxic legacy issue for Australia that largely flies under the radar, despite it being one of Australia's biggest waste problems and a huge risk to human and environmental health,” report author and EJA lawyer Bronya Lipski said.

“Coal ash dumps are a ticking time bomb. All Australian governments need to act now, not wait for a disaster.”

The group says there are dumps in Victoria, NSW, Queensland, WA and SA, and that the ash accounts for nearly one fifth of Australia's waste stream.

Coal ash contains toxic heavy metals linked to asthma, heart disease, cancer, respiratory diseases, nervous system damage and stroke.

“At most coal-fired power stations, coal ash is mixed with saline wastewater and pumped into enormous dump sites creating a lethal cocktail of mercury, lead, arsenic, selenium and chromium,” the report reads.

“This toxic slurry can leak into aquifers and soil needed by farmers and the environment, and into rivers and lakes where our families fish and our children swim.

“When it is left to dry out, winds can blow the toxic dust onto nearby communities where people breathe toxic pollution deep into their lungs.”

The report makes a range of recommendations, call for government inquiries, creating national rehabilitation plans, improving groundwater regulations and ensuring financial security from energy companies.