Action has been taken and improvements being made following the grisly discovery of more than 50 dead fish at a Hawke's Bay lake over the weekend.

On Monday nearly 70 eels were moved from Lake Waikapiro to the neighbouring Lake Tutira by Hawke's Bay Regional Council staff, and members of the Maungaharuru Tangitū Trust and Fish & Game.

This was to ensure the eels did not suffer the same fate as more than 50 trout, and countless bullies that appeared to have died from a lack of oxygen, a result of an algal bloom dying off.

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HBRC water quality scientist Dr Andy Hicks said staff spent half a day hopping from a boat to chase and capture the eels, before popping them into a barrel to transfer to Tutira.

Oxygen levels in the water made the eels "groggy and slow" so they were easier to catch, "which is handy when you're trying to do a trap and transfer, but it's a bit sad."

Fish and Game Hawke's Bay regional manager Mark Venman, who helped on Monday, said they had discovered another three dead juvenile rainbow trout, and more dead bullies.

The trout would be kept for further analysis to examine their growth rates and condition in this lake over recent years.

An air curtain was installed in the lake at the end of September as part of Te Waiu o Tutira (The Milk of Tutira) partnership project. It was designed to reduce algal blooms but one was already present in the lake before the trial started.

Although the lake's clarity had improved since Monday - from 1.4m to 2.8m - oxygen levels were not improving as quickly as hoped.

Yesterday's surface water levels were at 17 per cent, up 7 per cent from Monday. Levels at the bottom were one per cent higher than Monday's two per cent.

Levels should ideally be over 50 per cent. They were expected to recover as organic material in the lake broke down.

Prior to this, the air curtain had early success. Mr Venman said it would take a full season to determine how effective it was, "but this is a start."

The area is one of six identified in the HBRC's annual plan as environment hot spots needing attention.