Marshfield’s busiest day of the year, July 3, is just around the corner, and the town’s police, fire and public works departments are preparing for the festivities during the long Fourth of July weekend.

Police Chief Phil Tavares estimated about 100,000 people will be in town on July 3 alone.

With that influx of visitors comes increased traffic, and with alcohol flowing at parties around town, police will be mostly concerned with drinking and driving, as well as fights and other altercations, he said.

“You’ve got mixed crowds, and there’s fights, there’s underage drinking,” Tavares said. “There’s so many laws that are being broken, you’ve got to concentrate your efforts on the most serious, and the ones that are endangering the public.”

In the past there have been more than 100 arrests on July 3, but over the holiday weekend in 2015, police made 18 arrests, placed one person in protective custody and issued one summons.

“We would be more than pleased if we didn’t have to arrest anyone for the entire weekend,” he said.

More than 50 law enforcement officers, including 41 Marshfield police officers and permanent intermittent officers, Plymouth County deputy sheriffs and matrons for female arrests will be on patrol throughout the weekend in transport vans, marked and unmarked cruisers, on motorcycles, ATVs and on foot. Marshfield’s K-9 Beny will be on duty as well.

Tavares said all his officers will be on duty July 3 until the early morning hours of July 4, when activity tends to wind down. Some officers will even work a 16-hour shift from 4 p.m. July 3 until 8 a.m. July 4.

In addition to watching the roads and keeping tabs on parties, police also have to keep an eye on Marshfield’s waterways, where boating or swimming in the dark or while drinking can lead to dangerous situations.

“Alcohol and water don’t mix well. Some of our concerns, in addition to drinking and driving with motor vehicles, are with boats,” Tavares said.

Harbormasters will be on patrol throughout the weekend, looking out for accidents or people in the water. Police also have to be aware of riptides and children who have been separated from their parents at the beach.

Getting a different point of view helps police keep things under control as well: They can get a birds’ eye view with help from the Marshfield airport to spot missing people or track a suspect, while the harbormasters’ view from the sea helps them spot illegal beach fires.

Fire Chief William Hocking said bonfires and illegal fireworks are among his department’s biggest concerns around July 4.

“If we do see one, or someone calls about one, we have to go down to the beach and put it out,” he said of illegal fires, later adding, “It doesn’t make the people who are celebrating happy, but it is something we have to do.”

Police officers on ATVs will roam the beaches looking for stockpiles of wood, which indicate a future bonfire. The DPW then removes those stockpiles with a front-end loader, if necessary.

“We stay ahead of it and try to prevent it as much as possible,” Tavares said.

Over the course of the holiday weekend, the fire department will be fully staffed, meaning 13 firefighters will work each day and night, Hocking said. On July 3, two roving brush trucks will patrol beach areas in case they are needed, and Hocking and Deputy Chief Bud Cipullo will be out and about as well.

Traffic and maintaining its flow is another top priority for all three departments. Police and public works keep traffic moving so fire trucks and ambulances won’t be impeded.

DPW highway foreman Jimmy Kent said it’s almost impossible to travel in Brant Rock, Green Harbor or Rexhame in particular on July 3.

Starting around 7 or 8 p.m., DPW crews use cones and signs to set up additional travel lanes to accommodate the mass departure out of town and reroute access heading in, which is less voluminous. Traffic control assistant foreman Jim Jackson estimated workers place about 300 cones around Marshfield that day alone.

Drivers coming into town around that time may be diverted down side streets in order to free up major arteries like Ocean, Plain and Webster streets, which are used to move traffic out of town. Officers will also be directing traffic in certain areas, including outside CVS Pharmacy at Ocean and Webster streets and at the intersection of Ocean and Moraine streets. Traffic signals will be on flash at both locations.

The DPW works closely with Marshfield Police Safety Officer Kevin Feyler to make traffic flow smoothly through town, Kent said.

“We just listen to Kevin and do what he asks us. He’s the safety officer, and we try to keep everything safe,” he said.

Slow traffic is an inconvenience, but not necessarily a bad thing, as it keeps things under control, Tavares said.

Drivers need not only be mindful of how they drive, but where they park: Illegal parking is an issue around July 4, particularly on narrow streets where rows of parked cars can impede emergency vehicle access. Drivers should also be cautious not to block hydrants, Tavares said.

Given the number of moving parts and volume of people flooding in then out of town, Hocking said constant communication between the three departments is key to keeping things running smoothly.

“In my opinion, that’s the biggest reason we’re so effective,” he said.

Last year, a brush fire broke out near Humarock as traffic moved out on one of the busy days around the holiday. The fact that the departments cooperated to keep traffic moving allowed fire crews to get there in time and knock down the fire, Hocking said.

“It’s extraordinary that we move that number of people through and around town, and still keep emergency access open,” he said.

Overall, Tavares encouraged visitors and residents to enjoy their celebrations, but just do so sensibly by not drinking and driving, or driving while distracted, and remembering that setting off fireworks and drinking in public are illegal.

“We just want people to be safe while they’re enjoying our natural resources,” he said.

Follow reporter Hannah Sparks on Twitter @MarinerHannah