Guide

Go seeLandscape

River herring climb fish ladders in spring

April to May

Each spring millions of river herring swim in from the ocean and push up coastal rivers to the fresh water where they hatched. At a fish ladder you can watch them dart up the steps in quick bursts, one pool at a time.

Why this time of year

The Division of Marine Fisheries says alewives spawn from late March to mid-May and blueback herring from late April through June, once rivers warm enough. Its viewing guide gives best dates from early April through May at nearly every fishway, and timing shifts with the year's water temperatures.

How to notice it

  1. Open DMF's River Herring Viewing Guide and pick one of its 15 fishways near you. Each one lists its best viewing dates.
  2. Go on a bright day and look down into the pools of the ladder, or into the stream just below the dam, for dark fish about 10-12 inches long holding against the current.
  3. Watch one step of the ladder. Herring rest in a pool, then shoot up to the next one in a fast burst.
  4. Look but do not take: DMF prohibited river herring harvest in 2006 out of concern over their status.

Try this with kids: Pick one pool of the ladder and count how many fish jump up to the next step while you count to sixty.

Phrase to know: A “fish ladder” is a staircase of small pools that lets fish get past a dam.

Safety

  • Fishways sit at dams where water moves fast. Stay behind railings and keep children and dogs back from the edge.

Sources

  • web.archive.orgRead 2026-11-10 (archived copy of the DMF page; mass.gov itself returned 403). Last updated April 15, 2026. 'Each spring, MILLIONS of river herring migrate into Massachusetts waters'; 'This guide offers information on 15 of our state's busiest fish passage locations.' 'Alewife spawn in late March to mid-May, when water temperatures reach 51ºF. Blueback herring spawn in late April through June when water temperatures reach 57ºF.' Ideal viewing dates by site range from 'April 1 - May 1' to 'May 1 - June 15'. 'River herring can swim very fast in short bursts to pass up the ladder, making for a spectacular show!' 'Massachusetts has over a 100 separate river herring runs!'
  • web.archive.orgRead 2026-11-10 (archived DMF page). 'Females spawn in the spring and can lay up to 300,000 eggs.' Returns to natal streams at 3-4 years and about 12 inches. 'Recreational and commercial harvest of alewives was prohibited by DMF in 2006 out of concern over their status.'
  • web.archive.orgRead 2026-11-10 (archived DMF page dated April 7, 2025). 'Recreational and commercial harvest of river herring was prohibited in Massachusetts in 2006 out of concern over their status.' 'Blueback runs are less common than alewife runs in Massachusetts.' Back and upper sides 'tend to be a bluish color'.
  • web.archive.orgRead 2026-11-10 (archived DMF news, 7/02/2025). DMF calls Stony Brook 'one of the most visited "herring parks" in Massachusetts, with generations of families holding fond memories of seeing herring'; a 2025 restoration run was first seen April 30 and 'a large movement of river herring' passed another new fishway 'during the first week of May'.
  • asmfc.orgRead 2026-11-10 (ASMFC-hosted DMF plan, primary). 'River herring harvest in Massachusetts has been prohibited since 2006 due to concerns over declining stocks.' The plan's objective 'is to allow a reopening of the recreational river herring fishery in the Nemasket River'; the local commission 'elected not to open harvest' when first approved (2017).

Checked against these sources on November 10, 2026.

In the guide for April, May

Also worth noticing