In 2019, New York deployed 4.5 million pounds of retired Mill Basin Drawbridge materials at Hempstead Reef off Long Island’s South Shore, adding to the artificial reef

Ever been stuck on a bridge in rush-hour traffic and wondered what happens to these things when they are finally retired? Demolition, a landfill, a quiet, faded exit from the maps? For one Brooklyn crossing, the fate was more dramatic, and a lot wetter. According to a 2019 New York State Department of Environmental Conservation bulletin, crews sank 2.3 million pounds of the former Mill Basin Drawbridge, including its gatehouse building and bridge-support concrete, at Hempstead Reef earlier that year. That raised the Mill Basin total to 4.5 million pounds. At the time of that 2019 deployment, the reef site spanned 744 acres and sat about three nautical miles from the South Shore of Long Island; the site has since been expanded to 850 acres under New York's ongoing reef program. It's almost too convenient: aging infrastructure gets a second life. But convenient stories deserve a second look, so here is what the bridge-to-reef proposal offers, and what researchers believe.

From the Belt Parkway to the ocean floor

New York's Department of Environmental Conservation states that the original Mill Basin Drawbridge opened in 1940 as part of the Shore (Belt) Parkway bridge system crossing Mill Basin in Brooklyn. The 2019 pieces went down at Hempstead Reef, which has depths of up to 72 feet. That 2019 deployment was only the latest step in a much larger, multi-year effort: New York had been expanding its 12 artificial reefs statewide since 2017 as part of what the state called its largest artificial reef expansion initiative in its history, moving decommissioned infrastructure to reef sites across the coast rather than sending it to landfills.

Within that broader program, Hempstead Reef specifically had already received at least two decommissioned Erie Canal vessels, bridge trusses, and material from the former Tappan Zee Bridge in August 2018, with material from the old City Island Bridge in the Bronx following that December; so the Mill Basin pieces joined a site that was already, by design, a repository for retired New York infrastructure, not a one-off dumping ground. Imagine a secondhand shop for infrastructure, with the Atlantic Ocean as the customer.

Why fish might like a bridge

The state's pitch is straightforward: the structures are to provide finfish and crustaceans with shelter and food sources, and it names tautog, fluke, black sea bass, scup, and lobster,s which are expected to benefit. The wider science around this is positive, with fine print. According to a 2020 review article titled "Meta-Analysis Reveals Artificial Reefs Can Be Effective Tools for Fish Community Enhancement but Are Not One-Size-Fits-All," published in the journal Frontiers in Marine Science, an analysis of 39 studies showed that artificial reefs supported fish density, biomass, species richness, and diversity up to that of natural reefs. Concrete reefs supported higher fish density. However, the authors stress that results differ by location and material, and that reefs need to be approached strategically and according to a locality assessment.

The key question that won't go away: attract or produce?

To help see that, a critical eye on this is also valuable. A crowded reef is not necessarily a reef that creates fish. In a 1989 research article titled "Are High Densities of Fishes at Artificial Reefs the Result of Habitat Limitation or Behavioral Preference?," published in the Bulletin of Marine Science, J. Bohnsack laid out that reefs may simply attract fish because of their behavioral preferences, and not increase the overall production.

Per Bohnsack's 1989 review, evidence of increased production was largely anecdotal and deficient at the time, with one exception, and he wrote that artificial reefs were unlikely to benefit heavily exploited or overfished populations without additional management. This paper is over three decades old, and the research has continued. Nevertheless, the distinction is a useful lens: density and biomass reveal to some extent who is living on a reef, not where fish originate.

Who's cheering, and why

New York's Department of Environmental Conservation notes that the site promotes recreational fishing and diving, and supports the local economy, the then-Commissioner Basil Seggos said the work would "boost the economies of New York's coastal communities." But keep in mind: that's a description of the goals, not an independent finding. Worth noting: the department's acreage figure for Hempstead Reef has grown since that 2019 announcement. Its current artificial reef guide lists the site at 850 acres, up from the 744 acres on record at the time of the Mill Basin deployment, reflecting the site's continued expansion under the same statewide program rather than a factual inconsistency.

Turning a retired drawbridge into fish real estate is creative reuse, and the research shows well-designed artificial reefs have good metrics to withstand natural reefs. However, this is not a panacea; Bohnsack's framework shows that a reef's performance relates to the species, location, and fishing pressure involved, and the 2020 analysis is explicit that not all designs are one-size-fits-all. So the next time you are crawling across a bridge, it's worthwhile to consider its afterlife beneath the waves.