April 5 (Reuters) - Crews were working around the clock on Monday to prevent the collapse of a waste water reservoir's leaky containment wall near Tampa Bay, Florida, making steady progress after officials warned of an imminent threat of flooding over the weekend.

The U.S. Army Corps of Engineers was working alongside local emergency management crews to drain waste water from the Piney Point reservoir, which holds about 480 million gallons, in an effort to avoid a breach that could have flooded the surrounding area with a 20-foot wall of water, officials said.

Florida Governor Ron DeSantis declared a local state of emergency on Saturday over concerns that stacks of phosphogypsum waste, primarily from fertilizer manufacturing, could collapse and cause dangerous flooding at the site, which is a former phosphate plant.

The situation was improving on Monday as the coordinating agencies had managed to ramp up a pumping system that was draining polluted water from the property, which is owned by a company called HRK Holdings, to Port Manatee, acting Manatee County administrator Scott Hopes told reporters at a news conference.

"By the end of the day today when the additional pumps come online, we will more than double the volume of water that we're pulling out of that retention pool," Hopes said, adding that there were still just under 300 million gallons of water in the reservoir. "We should be looking at anywhere from 75 to 100 million gallons a day."

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A representative for HRK Holdings could not immediately be reached for comment.

At least 30 local residents had been evacuated to hotels for shelter as the drainage effort continues, Manatee County Public Safety Director Jacob Saur told reporters on Monday.

Officials say the drainage is necessary to ease pressure on the retaining wall and avoid the catastrophe of a sudden breach. But environmental advocates worry that pumping nutrient-dense water into Port Manatee will cause ecological trouble, including possibly spawning algal blooms that could kill marine life in Tampa Bay.

"The biggest concern from our standpoint right now is the amount of nutrients being loaded into the lower Tampa Bay," Ed Sherwood, executive director of the Tampa Bay Estuary Program, told radio station WMNF on Sunday. "This event, in probably five to 10 days, is introducing the amount of nutrients into the bay that we would want to see over an entire year."

U.S. Representative Vern Buchanan, a Republican who represents Florida's 16th district, told reporters on Monday that reducing possible ecological harm from the draining was a top priority and that the Environmental Protection Agency was working with local officials to monitor and mitigate the situation.

"Just the fact that we're running water into the Tampa Bay is not a great thing," Buchanan said. "But the reality of it is, it seems like it's the right thing to do right now."

(Reporting by Gabriella Borter; Editing by Steve Orlofsky)