This 1915 photograph shows the outlet of the Merrimack Mills Print Works.  In addition to making cotton textiles, the mills also bleached and dyed the yarn and finished cloth - nearly 100 million yards every year. Organic pollution accounted for some of the waste, such as natural dyes included madder (red), logwood (black or brown), and peachwood (red). The dying and printing of textiles required the use of mordants (chemicals used to affix the dye to the cloth), including inorganic chemicals like sulfuric acid, muriatic acid, lime, and arsenic. Only small amounts of dye and mordants were absorbed into the cloth, the bulk of the chemicals were dumped in the river causing the water to be discolored. 

Even though it was made illegal by an 1878 state law (excepting the entirety of the Merrimack River and Lowell's portion of the Concord River), the practice of dumping continued into the late 20th century. The Nyanza textile dye production facility dumped mercury-polluted wastewater into the Sudbury River, part of the Merrimack watershed, from 1917-1978 and is now classified as a US EPA Superfund Site.   

Kyanization is the process of treating wood with mercuric chloride (mercury) to make it resistant to decay. This photo shows the Kyanizing plant in Lowell, built in 1848, situated along a canal.  The mercury-treated wood was used in the construction of canals, gatehouses, bridges, and other structures submerged in water. This plant operated into the early 20th century. Today, mercury continues to leach from this wood into Lowell’s waterways, though the major source of mercury pollution throughout the country is from airborne emissions.   

By the 1870s, Lowell's mills began to supplement and replace their water-powered turbines with coal-fired furnaces. A sea of smokestacks began rising above Lowell's factories. The smoke released from these stacks contained mercury, which could remain airborne and travel hundreds of miles in the atmosphere, or it could drop to the ground with raindrops or as dust where it was absorbed by plants and soil, eventually entering the Merrimack watershed. Mercury found in Lowell might have come from the Midwest, and mercury emitted in Lowell might end up in the middle of the Atlantic Ocean – making it a problem requiring cooperation across geographic boundaries.  

Factories relied on lumber for construction and as fuel for the fires that provided energy for the steam-powered equipment and heating systems. Construction of one mill complex could consume hundreds of acres of trees. By the 1870s, deforestation, or the clearing of forests by humans, resulted in a shortage of old-growth lumber. Deforestation threatens watershed health by increasing the risk of floods and drought. 

English settler colonists stole New England's forests from indigenous communities and cleared the land for farming. They used the timber in shipbuilding, to make railroad ties, to burn for lime and brickmaking, and turned it into charcoal for ironworking. Their immediate needs and uses over-shadowed consideration of wider area impacts (run off, nutrient imbalances, destruction of animal habitats) and longer time effects (completely altered ecosystems, loss of biodiversity, increase in greenhouse gases, and other land/water degradation, like soil erosion and flooding). 

The construction of new factories, housing, and businesses for the growing city required vast resources: clay dug out of the earth to make bricks, marshes filled in as building sites, and forests cut down for lumber to frame the buildings. As forests and vegetation gave way to buildings, streets, and sidewalks, the natural ability of plants’ roots to absorb water runoff and filter pollution disappeared, and any waste - soot, feces, chemicals - that ended up on the ground washed directly into the waterways.  

Before his experiment in living at Walden Pond, Thoreau traveled on the Concord and Merrimack rivers in 1839, recording the damage that the early years of the Industrial Revolution had done to the watershed and writing about it in his book, "A Week on the Concord and Merrimack Rivers."  

He notes, "Large quantities of lumber ... were annually floated down the Piscataquoag to the Merrimack...." He also noted that the construction of mill dams along the Merrimack and its tributaries impacted the seasonal migration of fish.  Claiming allegiance with the aquatic creatures, Thoreau declared his willingness to act on their behalf, "Who knows what may avail a crow-bar against that Billerica dam?"