The latest annual Catchment Health Indicator Program report for 2020, released on Monday, revealed more of the ACT's catchment areas were classified as fair or higher during the past year.

Of the 98 catchment areas, four were classified as excellent, 36 as good and 55 as fair.

There were just three catchments in the area that were classed as poor or worse, which included Kippax Creek, Tuggeranong Creek upstream of Isabella Pond along with parts of the Yass River.

The report was based on more than 1800 water-quality surveys carried out by more than 200 volunteers throughout the course of the year.

The 2020 report found there was one fewer catchment area classified as poor compared to the previous year, while there was two more counted as fair and one more as excellent compared with 2019 levels.

Reassuringly, the number of times volunteers went out to catchment areas only to find the waterway completely dry was just one-quarter of the levels seen in 2019.

However, some catchment areas were impacted by large amounts of debris in the waterways due to the Orroral Valley fire, much of it washed in from large rainfall in the aftermath of the blaze.

"The rain washed ash and debris into the rivers and turbidity and phosphorus levels went beyond what most Waterwatch kits were capable of measuring," the report said.

"Thick layers of ash-laden mud lining the riverbanks and smothering the river substrate was, and still is, a feature of our major rivers."

Despite this, many waterways across the territory improved in condition as the year went on due to high flows from rain and more favourable conditions after many years of drought.